The Spermatogenesis in Pentatoma up to the Formation of the Spermatid. 51 



been reviewed all the cases where centrosomes have been described 

 as arising from nucleoli, and there I endeavored to prove that as 

 yet no proof of such a genetic connection has been brought for any 

 case). 



We may then conclude that the masses of substance lying within 

 the conical nuclear projections, are very probably of nucleolar origin. 

 But here other questions arise, more difficult to ansv^er. What pro- 

 duces the conical projections — a force exerted by the centrosomes, or 

 the pressure of the nucleolar masses upon the nuclear membrane? 

 Then, why should the latter lie in both of these projections — has the 

 nucleolus become divided and its halves then become removed to 

 opposite poles by some centrosomal force ? Nucleolar mass and conical 

 projection almost always occur together, that is the only fact at hand, 

 and it is futile to discuss the question further until further facts are 

 forthcoming. 



As to the origin of the mantle fibres. The pole radiation first 

 appears, and is well marked before the mantle fibres can be found 

 (Figs. 153, 159). The latter arise within the nucleus before its 

 membrane has disappeared, and from the first their proximal ends are 

 connected with the centrosomes (Figs. 154—158). They appear to be 

 formed, in great part at least, of the linin threads of the nucleus, 

 though their proximal ends may be cytoplasmic. They are not pro- 

 ducts of the substance of the nuclear membrane, since they are quite 

 clearly marked before the solution of the latter; when the latter 

 structure does disappear, it is quite possible that some of its substance 

 becomes changed into pole fibres. Within the nucleus, throughout the 

 prophases, the chromosomes are connected by a linin network; in 

 cells at the periphery of the testicle this appears rather as a 

 coagulated, somewhat granular mass (Figs. 152, 153), probably caused 

 by too long action of the fixing reagents ; but in cells near the centre 

 of the testicle the network is well pronounced (Figs. 144 — 158). 

 Shortly before the nuclear membrane disappears a few linin threads 

 remain connecting the chromosomes, and these, which are found even 

 in the monaster stage, may be termed inter-chromosomal fibres (inter- 

 zonal fibres of Moore, '95). The remainder of the achromatic elements 

 within the nucleus gradually take up a peripheral position near the 

 chromosomes, and become arranged in the direction of the centro- 

 somes. These linin elements are at first ramified with anastomoses, 

 but subsequently become demarcated from one another. They may 



be seen connecting the chromosomes with the centrosomes, while the 



4* 



