. The development of the chick : an introduction to embryology. Embryology; Chickens -- Embryos. 192 THE DEVELOPMENT OF THE CHICK and the angle of the body-cavity; it consists of two parts, viz., the primary tubule and the supplementary part. It never pos- sesses a continuous lumen, though there is often a cavity in the supplementary part, which opens into the body-cavity through the nephrostome (Fig. 112 B). The pronephros of the chick is a purely vestigial organ, of no apparent functional significance. Its development is accord- ingly highly variable, and it often happens that the right and

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. The development of the chick : an introduction to embryology. Embryology; Chickens -- Embryos. 192 THE DEVELOPMENT OF THE CHICK and the angle of the body-cavity; it consists of two parts, viz., the primary tubule and the supplementary part. It never pos- sesses a continuous lumen, though there is often a cavity in the supplementary part, which opens into the body-cavity through the nephrostome (Fig. 112 B). The pronephros of the chick is a purely vestigial organ, of no apparent functional significance. Its development is accord- ingly highly variable, and it often happens that the right and left sides of the same embryo do not correspond. It is also of very short duration and is usually completely lost on the fourth day. The tubules in the fifth to the tenth somites, moreover. /}.Gr.. J>>/. Fig. 113.—Transverse section tlu-ough the fifteenth somite of the same embryo. pr'n. (14), (15), Pronephric tubules of the fourteenth and fifteenth somites, respectively. hardly pass the first stage when they appear as thickenings of the somatic layer of the somitic stalk; thus the Wolffian duct does not extend into this region, and the best developed pronephric tubules are confined to the tenth to the fifteenth somites. The pronephric tubules do not form jMalpighian corpuscles; but glomeruli develop as cellular buds at the peritoneal orifices of the posterior tu})ules, projecting into the coelome near the mesentery. Curiously enough these do not form at the time of greatest development of the tubules, but subsequently to this when the tulniles themselves are in process of degeneration. Moreover, they are extremely variable as to number, and degree of development. They appear to be best developed on the third and fourth days. They agree in many respects with the so-called external glomeruli of the pronephros of Anamnia, and should be. Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration a