46 CHIM^EROID FISHES AND THEIR DEVELOPMENT. 



The grouping of the yolk elements in the mature egg is somewhat irregular. 

 Sometimes "drifts" of germinal yolk underlie the coarse yolk; sometimes they 

 extend obliquely, admitting between them inbursts of coarser yolk. In general, at 

 the time of fertilization, the germinal yolk dips deeply down into the coarse yolk, 



36 



35 



Fig, 35. Section of fertilization stage, showing near the surface and at the side of the germinal area a sperm which has just gained 

 entrance. This is shown at .>, surrounded by a lighter area of germinal material. In the depression above the sperm is a mucus, 

 like mass which may represent in part the tail of the sperm. /, Middle piece. X 575. 



Fig. 36. Section of fertilization stage, showing deep entrance pit of a sperm. From the lowermost point arise branching rays. 



Fig. 37. Detail of section of specimen shown in fig. 34. From the path of a sperm astral rays branch in many directions, and at 

 various points (indicated by the dark points) new centers of radiation appear. 



Fig. 38. Detail of fertilization stage shown in fig. 34. The present section follows almost exactly the entrance path of a sperm. The 

 latter appears at .v, and it is seen that the entrance pit is a delicate tube extending downward in the direction of a sperm. Around 

 the latter appears a well-marked aster, and in this neighborhood, strung along a prominent ray of the aster, are a number of deeply 

 stained " centrosomes." A similar " centrosome " occurs near the lowermost point of the entrance tube of the sperm. 



forming a plug-shaped mass twice as deep as wide (fig. 34). This is possibly the 

 homologue of the Panderian nucleus figured in the shark egg ; certain it is, how- 

 ever, that the egg of Chimaera has not as clearly a marked series of tunics in its 

 yolk arrangement. 



