CHANGES IN REPRODUCTIVE CELLS OF FLASMOBRANCHS. 295 
(figs. 85, 86, 87), the body of which is filled with nuclear 
chromatin, and the neck of which is stopped with the archo- 
plasmic vesicle (fig. 85, a.v.). Beyond the chromatic flange 
the nuclear membrane encases the whole, much in the same 
way as the basket-work used to protect an Italian wine-flask, 
the nuclear sap between it and the chromatin representing the 
glass. 
42. The base of the intra-cellular part of the flagellum, with 
the centrosomes, now lies between the archoplasmic vesicle 
and the chromatic flange, but the point of attachment of the 
flagellum moves round the surface of the nucleus, the archo- 
plasmic substance penetrating the nuclear membrane, and 
resting with the base of the flagellum on the chromatin, in a 
funnel-shaped mass (fig. 85, a.). The centrosomes are no 
longer visible, being either lost or becoming indistinguishable 
among the rest of the chromatic substance at the base of the 
tail. The translocation of the point of attachment of the 
flagellum continues (figs. 86, 87) until it finally comes to 
rest at the side of the nucleus opposite to the neck and the 
archoplasmic vesicle where it started (fig. 88). The ‘ neben- 
kern” is implicated in this motion, and its substance is 
eventually mixed up with that of the true archoplasm, both 
structures forming a distinctly differentiated protoplasmic mass 
extending along the intra-cellular part of the flagellum, from 
its base in the nuclear chromatin to its exit through the nuclear 
wall (figs. 85—89, v.a.). The whole of this mass (composed 
of the “nebenkern’”’ and the archoplasm, together with the 
intra-cellular part of the flagellum) eventually forms the long 
Mittelstiick of the mature spermatozoon (figs. 90, m.). The 
origin of the Mittelstiick in these fishes will thus be seen to 
coincide with what I have related respecting this structure 
in Mammalia, and probably with Hermann’s description of its 
formation in Salamandra together with what occurs in a 
number of Invertebrate spermatogeneses. 
43, At the oppositeend of the nucleus the archoplasmic yoeiele 
(a. v., figs. 88, 89, 90) becomes first flattened, and then elongates 
out, together with the nuclear chromatin, forming. a definite 
