OF THE OEKM CELLS OF METAZOA. 



219 



chromosome of one generation is represented in a particular one of a preceding, so that 

 cliromosoin.es are not produced de novo in eacli generation. The evidence for tins assump- 

 tion, as regards the Hemvptera, has been already stated above (cf. the heading : " The 

 process of spermatogenesis in the Ilemiptera") ; other evidence was shown in my study 

 on r<ripatus (1901), and there also the observations of other workers was considered in 

 some detail so it is not necessary at this point to enter into these particulars. Without this 

 assumption, which is an actuality, as I have shown in some cases, it would be very diffi- 

 cult to determine the meaning of the stages of the germinal cycle; while on this assump- 

 tion much becomes clear, and the phenomena of the synapsis stage alone are strongly 

 corroborative of this assumption. 



Now in the cycle of the germ cells there is a chromosomal peculiarity which has been 

 described by other investigators, but its significance has not been understood ; 1 referred 

 to it in my study of Peripatus (1901). In the anaphases of the male and female pro- 

 nuclei, as in the anaphases of the early cleavage cells, it is characteristic that each chro- 

 mosome becames vesicular so that at this stage each daughter nucleus appears composed 

 of as many such vesicles as there are chromosomes. Each vesicle has its own limiting 

 wall, and not infrequently the different vesicles may he only loosely connected together; 

 ultimately, however, when the complete rest stage is attained, the boundaries between the 

 vesicles disappear so that the nucleus appears a whole without separated parts.* 



Riickert (1895) supposes the chromosomal vesicles to represent a shortened anaphase, 

 occasioned by the rapid sequence of the mitoses in the lilastomeres ; that this is hardly a 

 correct explanation is seen from the following considerations. From the list of cases just 

 mentioned in the footnote it will he seen that, anaphases with vesicular chromosomes are 

 found in the pronuclei and in the earlier cleavage cells — i. c, in nuclei at the beginning of 

 the germinal cycle. I have never seen such vesicular stages in the last generations of 

 ovogonia and spermatogonia, nor to my knowledge has any one else; but in these later 



* This vesicular stage of the chromosomes in Ihe anaphases of milosis lias been described by the following 

 workers, though this is probably not a complete list : Kennak (1855, cited by Henneguy, 18%, blastomeres of -BaJmc/iiit); 

 Oellacher (1872, egg of Trout); Trinchese (1875, cited by Henneguy, 1896, pole cells of Aeolididae); O. llertwig 

 (1870, id. citat., blastomeres of Bufo); Fol (1870, id. citat., Toxopneustes egg); Henneguy (1882, 1891, egg of Trout); 

 Bellonci (1884, cited by Henneguy, 1890, lilastomeres of Axolotl); Schwarz (1888, id. citat., blastomeres of Trout); 

 Van iler Htrieht (id. citat., larval epidermig'of Salamaudra and Triton, niegacai yocy tes, leucoblasts and erytbroblasts 

 of embryonic liver of Mammals); Mead (1895, 1898, Chmtopterus, female pronucleus and blastomeres up to 16-cell 

 stage); Foot (1894, 1897, female pronucleus of Allolobophora); Sobotta (1897, pronuclei and first cleavage of Amphi- 

 oxus); Kosta.nec.ki and Wierzejski ( IS90, male and female pronuclei of J'/iyna); v. Klinckowstrc'.ni (18B7, male and 

 female pronuclei of I'rosthoccratm); Kiickcrt (I S95, blastomeres of Cyclops); (). Schult/.e (1887, blastomeres of Axolotl); 

 Koelliker (1889, blastomeres of Siredon); Van Iieneden and Neyt (1887, blastomeres of Ascarn); Biilim (1888, male 

 and female pronuclei and first cleavage of Petromyzon); Wheeler (1897, female pronucleus of Myzostoma, occasion- 

 ally showing widely separated chromosomal vesicles); Coe (1898, female pronucleus and first cleavage of Cerebratulus); 

 Boveri (1888, blastomeres of AsQaris), 



