. The cell in development and inheritance. Cells. . Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the original work.. Wilson, Edmund B. (Edmund Beecher), 1856-1939. New York Macmillan

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RM2AJJ05R–The cell in development and inheritance . Fig. 7 — Spermatogonia of the salamander. [Meves.]Above, two cells showing large nuclei, with linin-threads and scattered chromatin-granules; ineach cell an attraction-sphere with two centrosomes. Below, three contiguous spermatogonia,showing chromatin-reticulum, centrosomes and spheres, and sphere-bridges. be surrounded; but it must be remembered that the cell-wall in somecases arises by a direct transformation of the protoplasmic substance,and that it often retains the power of growth by intussusception likeliving matter. It is unfortunate that some

RMPG1DFG–. Heredity in relation to evolution and animal breeding, . Heredity. THE DUALITY OF INHERITANCE products of the ori2:inal cell contain in each case two chromosomes, half the original number.. Fig. 5. — Diagrams showing the essential facts of chromosome reduction in the development of the spenn-cells. (After Wilson.) These chromosomes make up the bulk of the head of the sperm which forms from each of 17. Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly r

RM2AJG1XD–The cell in development and inheritance . vitelline membrane is, however, often formed soonafter fertilization, as in echinoderms. The most interesting featureof the plant-ovum is the fact that it often contains plastids (leuco-plasts or chromatophores) which, by their division, give rise to thoseof the embryonic cells. These sometimes have the form of typicalchromatophores containing pyrenoids, as in Volvox and many otherAlgae (Fig. 64). In the higher forms (archegoniate plants), accordingto the researches of Schmitz and Schimper, the q%% contains numer-ous minute colourless leucoplasts, whic

RM2AJFTCA–The cell in development and inheritance . n to believe that the follicle-cells are immediatelyconcerned with the conveyance of nutriment to the ovum. A num-ber of observers have maintained that the follicle-cells may actuallymigrate into the interior of the o.gg, and this seems to be definitelyestablished in the case of the tunicates and mollusks (Fig. 75).^Such cases are, however, extremely rare; and, as a rule, the materialelaborated by the nutritive cells is passed into the o^gg either in solu-tion or in the form of granular or protoplasmic substance.^ Aninteresting case of this kind occurs

RM2AJE7KF–The cell in development and inheritance . ^Tj) and Korschelt (89), both of whom have givenextensive reviews of the entire subject in this regard. Haberlandtsstudies related to the position of the nucleus in plant-cells withespecial regard to the growth of the cellulose membrane. He deter-mined the very significant fact that local growth of the cell-wall isalways preceded by a movement of the nucleus to the point of growth.Thus, in the formation of epidermal cells, the nucleus lies at first near PHYSIOLOGICAL RELATLONS OF NUCLEUS AND CYTOPLASM 347 the centre, but as the outer wall thickens, the

RM2AJHF2N–The cell in development and inheritance . Fig. 7 — Spermatogonia of the salamander. [Meves.]Above, two cells showing large nuclei, with linin-threads and scattered chromatin-granules; ineach cell an attraction-sphere with two centrosomes. Below, three contiguous spermatogonia,showing chromatin-reticulum, centrosomes and spheres, and sphere-bridges. be surrounded; but it must be remembered that the cell-wall in somecases arises by a direct transformation of the protoplasmic substance,and that it often retains the power of growth by intussusception likeliving matter. It is unfortunate that some

RM2AJFJTH–The cell in development and inheritance . (97) gives a somewhat different account of the process, believing that thering is derived from the mid-body of the last mitosis. Meves and McGregor have, however,shown that the ring and mid-body coexist in the early spermatids (Fig. 84), which seemsdecisive against Hermanns conclusion. ^ Hermann finds also the ring observed in the salamander, and believes it to be the mid-body. The middle-piece is regarded by him as a product of the spindle-remains, but onboth these points he is contradicted by Suzuki. 168 THE GERM-CELLS archoplasm of the spermatid. Su

RM2AJFJ1E–The cell in development and inheritance . s completely to the deeply staining corpuscle in the sper-matogenic cells of the Characeae, ferns, and Equisetaceae; that,furthermore, the middle-piece of the spermatozoon represents theband which bears the cilia of the plant spermatozoid, while the tail-like flagella^ of the salamander or mouse represents the cilia. ^ 1 QC p. 321. For the function of the centrosome in fertilization, see p. 208. 2 In the original Faden perhaps meant to designate the axial filament.« 97, 3- GROWTH AND DIFFERENTIATION OF THE GERM-CELLS 173 This tallies with Strasburgers

RM2AJG1JT–The cell in development and inheritance . ece is in some cases derived from an archoplasmic mass,representing an attraction-sphere {Lunibriciis) or a portion of theNcbcnkcrn (insects), and it contains, or according to some authorsactually arises from, the centrosome (salamander, mammals, insects,etc.). 4. The tail, or flagellum, in part, at least, a cytoplasmic productdeveloped in connection with the centrosome and archoplasm ? End-piece. Fig. 65. — Diagram of theflagellate spermatozoon. 136 THE GERM-CELLS (attraction-sphere or Nebenkern) of the mother-cell. It consistsof a fibrillated axial f

RM2AJE4WG–The cell in development and inheritance . the displacement of cells subsequent to division, we find, asin the case of the division-rhythm, obvious mechanical factors com-bined with others far more complex. The arrangement of tissue-cellsusually tends toward that of least resistance or greatest economy ofspace; and in this regard they have been shown to conform, broadlyspeaking, with the behaviour of elastic spheres, such as soap-bubbleswhen massed together and free to move. Such bodies, as Plateau 1 Cf. Wilson, 92, Kofoid, 94, Lillie, 95, Zur Strassen, 95, Ziegler, 95, and especiallyJennings,

$The cell in development and inheritance . , and hence corresponding to a Nebenkern {e.g. salaman-der, Meves, 96), and the distinction between Nebenkern and idio-zome here fades away. The idiozome is usually concerned in theformation of the acrosome (Amphibia, mammals), but sometimes seems ^ The English equivalent of this should be paranucleus, but the latter word has alreadybeen used in various other senses, and it seems preferable to retain Biitschlis original Ger-man word. ^ For critical discussion, see Erlanger, 97, I. 164 THE GERM-CELLS to degenerate without contributing directly to the sp Stock Photo$

RM2AJFKDK–The cell in development and inheritance . , and hence corresponding to a Nebenkern {e.g. salaman-der, Meves, 96), and the distinction between Nebenkern and idio-zome here fades away. The idiozome is usually concerned in theformation of the acrosome (Amphibia, mammals), but sometimes seems ^ The English equivalent of this should be paranucleus, but the latter word has alreadybeen used in various other senses, and it seems preferable to retain Biitschlis original Ger-man word. ^ For critical discussion, see Erlanger, 97, I. 164 THE GERM-CELLS to degenerate without contributing directly to the sp

RM2AJH861–The cell in development and inheritance . spindle-hbres, to be largely composed. In support of this may bementioned, besides the mode of formation of the partition-walls in the division of plant-cells, Harpers (97) very interesting observations on the formation of the ascospores inErysiphe (Fig. 33), where the spore-membrane appears to arise directly from the astralrays. 56 GENERAL SKETCH OF THE CELL focussed at the centrosome. On this basis he endeavours to explainthe position and movements of the nucleus, the succession of division-planes, and many related phenomena.^ Hatschek (88) and Rabl

RM2AJFRWD–The cell in development and inheritance . m and the formation of passive deutoplasm-bodies suspendedin the protoplasmic network. During the growth-period a peculiarbody known as the yolk-micleiLS appears in the cytoplasm of manyova, and this is probably concerned in some manner with the growth 1 See p. 338. 2 See McMurrich, 96. GROWTH AND DIFFERENTIATION OF THE GERM-CELLS 153 of the cytoplasm and the formation of the yolk. Both its origin andits physiological role are, however, still involved in doubt. The deutoplasm first appears, while the eggs are still very small,in the form of granules wh

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