THE EGG-CAPSULE. 



41 



Before describing the various stages of Chimsera (C. collici) a brief survey of 

 the general plan of development might be given {cf. Biol. Bulletin, 1903, vol. iv. 

 No. 5, pp. 270-286): 



The development is shark-like (figs. 24-29). In early stages a small germinal 

 area is present. In this polyspermy occurs, then a cleavage, in which, however, 

 surface furrows are retarded. The early gastrula suggests somewhat closely the 

 condition in shark, or rather in ray, but the blastopore appears near instead of at 

 the margin of the blastoderm. The embryo develops a long, delicate tail, external 

 gills, and a head terminating in a conspicuous frontal "lobe." It absorbs the yolk- 



Figs. 27-29. — Egg-capsules of Chimaera colliei, partly opened, so as to show egg and young. Natural size. 



27. Early embryo (about 32 days), showing subdivision of yoIL material. 



28. Late embryo (about 5 months), showing external gills and miniature sac. At this time the embryo is bathed in a heavy milky fluid resulting 



from continued subdivision of yolk masses. 



29. Young Chimaera at about the time of hatching l> eight months). The capsule at this period is greatly weathered and develops a tension 



which probably aids the operculum in springing open and permitting the young to escape. 



sac, and before hatching becomes large in size and has many features of the adult, 

 e. g., mixipterygia in the case of the male. By far the most remarkable feature 

 during this process of development is the behavior of the yolk. This undergoes 

 vacuolization, followed by fragmentation. Of the yolk a small portion only is 

 inclosed within the sac of the young ; the remainder continues to fragment, form- 

 ing a creamy mass which nourishes the embryo via external gills and gut. 1 he 

 fragmentation, we have reason to believe, is an extreme modification of the process 

 of cleavage. 



