68 SYDNEY J. HICKSON. 



In some Annelid worms the nucleus of the spermatogonium 

 disappears, and there is no evidence at present that the nuclei 

 of the spermatocytes are derived by repeated mitotic divisions 

 of this nucleus (Jensen, 28, and others). In the recent work 

 on spermatogenesis, by Pictet (47) no mention is made of the 

 manner in which the nuclei of the spermatogonia divide in 

 Polychsetes.^ 



A study of the literature of spermatogenesis shows that 

 when there is a distinct division of the protoplasm to form the 

 spermatocytes or spermatogonia, distinct karyokinesis of the 

 nuclei may generally be seen; but when, on the contrary, 

 multinucleated cells are formed, which eventually give rise to 

 the spermatocytes, the nucleus of the spermatogonia either 

 disappears or divides amitotically. 



It is not necessary for me to discuss in detail the numerous 

 cases of indirect fragmentation of the nucleus that have been 

 described by Arnold in his numerous papers in 'Virchow's 

 Archiv ' and the ' Archiv fiir mikroscopische Anatomic,' by 

 Werner (61), Schottlaender (50), Hess (26), Geelmuyden (13), 

 Beltzow (2), Strobe (54), Goppert (15), and others. Many of 

 these cases are those of the nuclear division of giant-cells, and I 

 believe I am quite correct in saying that in all of them the 

 fragmentation of the nucleus is not immediately followed by 

 cell division. 



The general conclusions to be drawn from the evidence 

 before us are — 1. That fragmentation of the nucleus is a 

 normal method of nuclear division, and is not always a sign 

 of pathological change. 2. That in many of the instances in 

 which the nucleus is supposed to disappear there is, as a 

 matter of fact, minute fragmentation. 3. That fragmentation 

 only occurs where there is no cell division ; and 4. That 

 karyokinetic division of the nuclei is caused by the forces in the 

 cell protoplasm which bring about the division of the cytoplasm. 



That there may be many forms of nuclear division inter- 



' It is a noteworthy point that 0. von Eath (48), who believes that the 

 nuclei of the spermatogonia and spermatocytes always divide mitotically, does 

 not refer at all in his paper to the spermatogenesis of Polychsetes. 



