OF THE GERM CELLS OF METAZOA. 219 



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

 chromosomes are not produced de novo in each generation. The evidence for this assump- 

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

 process of sperm atogenesis in the Hemiptera ") ; other evidence was shown in my study 

 on Peripatus (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 ; I 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 be 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 blastonieres ; 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 be seen that anaphases with vesicular chromosomes are 

 found in the pronuclei and in the earlier cleavage cells i. e., 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 the anaphases of mitosis has been described by the following 

 workers, though this is probably not a complete list : Remak (1855, cited by Heuneguy, 1896, blastomeresofBafracAta); 

 Oellacher (1872, egg of Trout); <Trinchese (1875, cited by Ilenneguy. 1896, pole cells of Aeolididae); O. Hertwig 

 (1876, id. citat., blastonieres of Bufo}; Fol (1879, id. citat., Toxopneustei egg); Henneguy (1882, 1891, egg of Trout); 

 Bellonci (1884, cited by Heuneguy, 1896, blastomeres of Axolotl); Schwarz (1888, -id. citat., blastomeres of Trout); 

 Van der Stricht (id. citat., larval epidermic of Salamandra and Triton, megacaryocy tes, leucoblasts and erythroblasts 

 of embryonic liver of Mammals); Mead (1895, 1898, Chaitopterus, female prouucleus and blastonieres up to 16-cell 

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

 oxus); Kostanecki and Wier/ejski (1896, male and female pronuclei of Physa); v. Klinckowstroui (1897, male and 

 female \>Toanc\eiof Prosthoceraus); Riickert (1895, blastomeres of Cyclops); O. Schultze (1887, blastomeres of Axolotl); 

 Koelliker (1889, blastomeres of Siredon); Van Beneden and Neyt (1887, blastomeres of Ascaris); Bourn (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 Cerebratului) ; 

 Boveri (1888, blastomeres of Atcarit), 



