2/4 BASHFORD DEAN. 



however, a rate of development proportionate with that of known 

 egg-depositing elasmobranchs I infer that an embryo of five 

 inches can hardly be younger than nine months (Fig. 7). An 

 estimate of a total incubation of twelve months in this species 

 would hardly be excessive. 



Fertilisation. Fertilization is shark-like. Polyspermy occurs 

 and a similar number of merocyte nuclei ; the conjugation of the 

 pronuclei occurs at a similar niveau in the germinal area, the 

 male pronucleus passing through the germinal protoplasm and 

 then approaching the female pronucleus from a lower plane. 

 Also similar are the location and behavior of the merocyte 

 nuclei during early cleavages. Different from shark, however, is 

 the longer duration of the period of the entrance of the sperm 

 (a newly-entered spermatozoon being present in a preparation 

 showing fusion of pronuclei), and the clearness with which sperm 

 paths are to be noted. Of the latter the surface pits can be 

 seen under low powers. The germinal area is also notably 

 deeper than in the shark. 



Segmentation. As in Torpedo (Riickert) and certain other 

 elasmobranchs the appearance of cleavages at the surface of the 

 germinal area is retarded, the first surface furrow appearing about 

 the time of the third or fourth nuclear division. In connection 

 with the furrows at their deeper rim are vacuoles (as in Fig. 8 



FIG. 8. Early segmentation. Section through middle of germinal area. At A 

 a fissure-like vacuole becomes continuous with an intercellular space. / about 30. 



at A) which pass into the yolk, and suggest a former condition 

 of deeper cleavage. This inference that the fissure-like vacuoles 

 are to be interpreted as potential but semi-suppressed cleavage 

 spaces is well borne out by the structures of a later stage (Fig. 9) 

 in which the vacuoles are shown to be patently continuous with 

 intercellular spaces, and in which nuclei occur in the underlying 

 germinal masses. It is also to be inferred that a further degree 



