PLATE VIII. 

 EMBRYOS OF CHIMERA COLLIEI. 



ch. Notochord. sp. Spiracle. 



. Neural tube. x. Irregularity in line of postanal gut. Possibly artifact. 



n. c. Neurenteric canal. y. Yolk. 



p. a. g. Postanal gut. y. s. Stalk of yolk-sac. 



Fig. 42 c. Ventral aspect of the head region of specimen shown on plate vn, fig. 42. This indi- 

 cates especially the extent of the stomadeal invagination. 



Fig. 46 a. Detail of tip of tail of specimen shown in plate vn, fig. 46. It illustrates especially the 

 character of the caudal knob and the extent of the postanal gut. 



Fig. 47. Embryo and blastoderm shown attached to irregular mass of yolk. The embryo is of the 

 stage shown in plate vn, fig. 44. It will be seen that a deep crease marks the line of sepa- 

 ration of blastoderm and yolk, y. 



Fig. 47 a, b. Figures showing the foregoing specimen in natural size. These give an idea of the 

 extent of the yolk mass around which the blastoderm is growing. 



Fig. 47 c. Margin of blastoderm in the region which, in fig. 47, is concealed by the tail. It is 

 here slightly nicked, and a line of fusion can be traced in the direction of axis of embryo. 



Fig. 48. Embryo of stage shown in plate vn, fig. 45. The blastoderm has by this stage almost 

 entirely inclosed the yolk mass noted in fig. 47. A small portion of the yolk is, however, 

 seen in lower part of figure. The figure also shows, although indistinctly, a line of fusion 

 passing from the embryo in the direction of the rim of the blastoderm. 



Fig. 48 a. Preceding specimen shown in posterior aspect. This indicates the extent to which the 

 rim of the blastoderm has inclosed the yolk. The irregularity in its margin is due 

 probably to artifact. In the yolk itself masses can be distinguished, even under a low 

 power, which suggest separate blastomeres. The exposed surface of the yolk is somewhat 

 irregular, suggesting that a portion of the yolk material has recently become detached. The 

 blastomeres themselves are loosely associated, so that some of them could be removed with 

 dissecting needles. Their peripheries are not quite as distinct as the present figure indicates. 



Fig. 49. Late embryo. Age unknown (probably five or six months), corresponding approximately 

 to Balfour's stage N in shark. Although this specimen was examined living, and was 

 apparently uninjured, its body cavity was filled with blood cells. Observe also the 

 enlarged blood-knots in the external gills and the position of the spiracle denoted in this 

 figure by the small red spot immediately above the rim of the upper jaw. (Embryo's 

 length 35 mm.) 



Fig. 49 a. Dorsal aspect of preceding specimen. This pictures more clearly the blood-knots of 

 the external gills. 



Fig. 49 b. Ventral aspect of preceding specimen. This shows especially the masses of yolk, y, 

 attached to the external gills; also the point of attachment of the stalk of the yolk sac, y. s. 



Fig. 49 c. Detail of facial region of preceding specimen, indicating the extent to which the gill 

 arches protrude at the side of the head. The gill filaments are cut away, but from their 

 bases one observes that they occur only on the anterior rim of each gill slit. 



Fig. 49 d. Lateral aspect of preceding specimen. This pictures again the gill region from which 

 the external filaments have been removed. The spiracle, sp., is seen immediately under 

 the eye. 



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