27 



to reproduce before the end of the summer. It would appear 

 that there is nothing comparable to this as far north as Culler - 

 coats, where breeding begins so much later. 



Ova. — The fully developed ova present in July are remarkable 

 for their immense size. They are more or less oval in outline, 

 except for an attaching pseudopodium to which I shall refer later. 

 The cytoplasm is granular and fan4y deeply staining. The 

 nucleus is large, vesicular, very faintly staining, with distinct, 

 eccentrically placed nucleolus stained almost black (Fig. 2). 

 These ova lie behind the flagellate chambers attached to the 

 gastral epithelium. 



Maturation and Segmentation. — In only one case have I 

 been able to find what I take to be the first maturation spindle 

 (Fig. 1), though the stage immediately following the extrusion 

 of the first polar body is rather more common. This stage is 

 shown in Figures 2 and 3, the second of these showmg the nucleus 

 aheady in the spireme stage of the second maturation division, 

 while Figure 4 represents the end of the division, the second polar 

 body havmg been cut off but not yet completely extruded from 

 the cj^toplasm. Figure 5 shows the second polar body. 



After fertihsation, total and equal segmentation takes place 

 up to about the seventh or eighth division (Figs. G and 7), after 

 which a small number of cells at one pole increase in size, become 

 more granular and divide much less quickly than the smaller cells, 

 which nov/ begin to elongate radially. The embryo becomes 

 convex at the pole occupied by the smaller columnar cells, and 

 flattened in the region of the granular elements (Fig. 8). 



The Pseudogastf.ula. — As development continues the 

 number of granular cells increases more quickly, but instead of 

 growing outwards they become temporaril}^ invaginated into the 

 segmentation cavity (Figs. 9 and 10), giving rise to the pseudo- 

 gastrula, the significance of which has given rise to so much 

 speculation. 



Writers on the subject vary greatly iii their views as to the 

 importance of this stage. Balfour attaches no importance to it, 

 whilst Sollas explains it as being an attempted reversion to an 

 ancestral type, and as suggesting affinities with the C'oelenterates. 

 Dendy (2), however, puts down its formation in G. lahyriirtliica 



