of Edinburgh , Session 1885-86. 
821 
Explanation of Diagiiam. 
The first line, A-F, exhibits types of ovum segmentation : — A, regular morula ; 
B, unequal segmentation, e.g ., in some Molluscs; C, centrolecithal type, e.g., 
in Peneus ; D, partial segmentation ; E, the same, with the cells less markedly 
defined off from the yolk; F, inverted gastrula or “ obgastrula ” form, e.g., 
in Teleosteans. 
In the next two lines various types of spermatogenesis are collated with the 
above to illustrate the parallelism : — A' and A", morula type, as in Sponge, Tur- 
bellarian, Spider, &c. ; B' and B", where the division is unequal, and one large 
nutritive cell is seen (Plagiostome fishes, Yon la Yalette St George); C' and C", 
after Blomfield, Jensen, &c., showing central cytophoral or blastophoral 
nutritive portion; D' and D", sperm -blastoderm, with a few formative cells 
on large nutritive blastophore, after Gilson, &c. ; E' and E", the same, with 
the sperm cells less definitely separated off, after Yon Ebner and his followers ; 
F' and F", “ obgastrula type,” in which the nutritive portion has come to sur- 
round the formative cells, after Swaen and Masquelin, Renson, &c. (See Text. ) 
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