226 CONTINUITY OF THE GERM-PLASM AS THE [IV. 



into sperm-cells, as in Selachians, in the frog, in many worms 

 and snails, and also in mammals (Blomficld). But the attention 

 of observers has been directed to that part of the cell-body 

 which is not used in the formation of sperm-cells, rather than 

 to the nucleus ; and the proof that part of the nucleus also 

 perishes is still wanting in many of these cases. Fresh in- 

 vestigation must decide whether the nucleus of the sperm- 

 mother-cell perishes as a general rule, and whether part of 

 the nucleus is rendered powerless in some other way, where 

 such mother-cells do not exist. Perhaps the paranucleus 

 (Nebenkern) of the sperm-cell, first described by La Valette 

 St. George, and afterwards found in many animals of very 

 different groups, is the analogue of the polar body. It is true 

 that this so-called paranucleus is now considered as a con- 

 densed part of the cell-body, but we must remember that it 

 has been hitherto a question whether the head of the sperma- 

 tozoon is formed from the nucleus of the cell or from the 

 paranucleus ; and that the observers who held the former view 

 were in consequence obliged to regard the paranucleus as a 

 product of the cell-body. But according to the most recent 

 investigations of FoP, Roule -', Balbiani^, and Will*, upon the 

 formation of the follicular epithelium in the ovary of different 

 groups, it is not improbable that parts of the nucleus may 

 become detached without passing through the process of 

 karyokinesis. Thus it is very possible that the paranucleus 

 may be a product of the main nucleus and not a condensed 

 part of the cell-body. This view is supported by its behaviour 



simply speak of sperm-cells and spermatoblasts, and distinguish the 

 latter by numbers when they occur in successive generations ol' different 

 form ? Moreover, all the names which have been suggested for 

 successive stages of development, can only be applied to the special 

 group of animals upon which the obser\'ations have been made. Hence 

 great confusion results from the use of such terms as spermatoblasts, 

 spermatogonia, spermatomeres, spermatocysts, spermatocytes, spermato- 

 gemmae, etc. 



* Fol, ' Sur I'origine des cellules du folliculc et de I'ovule chez les 

 Ascidies.' Compt. rend., 28 mai, 1883. 



' Roule. * La structure de I'ovaire et la formation des oeufs chez les 

 Phallusiadees.' Ibid., 9 avril, 1883. 



' Balbiani, ' Sur I'origine des cellules du follicule et du noyau vitellin 

 del'Geufchez les Geophiles.' Zool. Anzeiger, 1883, Nos. 155, 156. 



* Will, ' Ueber die Entstehung des Dotters und der Epithelzellen bei 

 den Amphibien und Insecten.' Ibid., 1884, Nos. 167, 168. 



