os the large nucleus behind. 
1880, | A Sketch of Comparative Embryology. 105 
spherical shape and finely granular appearance. The daughter 
nuclei multiply by division. While these changes, occur, the 
whole cell or spermatocyst becomes greatly elongated. At the 
completion of this stage, the parent nucleus at the inner end of 
the cell disappears, and a nucleus similar in appearance appears 
at the outer end, £ It is probable, but not demonstrated, that 
the two nuclei are identical, in other words, that the parent nucleus 
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Fic. 8.—Development of the spermatozoa in sharks, after Semper. 
‘Migrates from one end to the other. The upper nucleus hence- 
forth is passive, remaining behind to degenerate after the sper- 
matozoa have been discharged from the cyst. Each one of the 
daughter nuclei, after subdividing still further so as to become 
very small, g, gathers a distinct mass of protoplasm around itself, 
and becomes a spermatoblast. The further development proceeds — = 
by alteration of the shape of these bodies: the nucleus elongates, 
becomes S-shaped, 4. The elongation advances, the nuclei become _ 
Straight and rod-like, and lie parallel to one another in the upper 
end of the cell, ù If we look at the cells from the outer surface 
of the ampulla, the center of the end of each cell is occupied bya 
cluster of dots corresponding to the bundle of rod-like nuclei — 
seen endwise, #. Each long nucleus forms a spermatozo6n head, ee 
_ Which is connected with a thread-like tail. The development is o 
completed by the discharge of the bundle of spermatozoa, leaving a 
The essential feature of this whole history is, that a ett 
