M'CLUNG : SPERMATOCYTE DIVISIONS OF THE ACRIDID.E. 99 



With the ingrowth of a cell wall, the second spermatocytes separate 

 and produce the spermatids, and these transform directly into sper- 

 matozoa. 



8. The sequence of the longitudinal and cross-divisions appears to 

 be constant. There is reason to believe that it is of fundamental im- 

 portance, and, therefore, accounts of the indiscriminate occurrence of 

 both forms in the same cell generation should be accepted with cau- 

 tion. If the polar body of the parthenogenetic eii^v acquires new 

 properties by its brief separation from the egg which it subsequently 

 fertilizes, there is every reason to suppose that the order of chromatid 

 separation in the forming spermatozoa is vital and essential. 



9. The accessory chromosome is a constant and important element 

 of the germ cell. It arises, in the Acrididae, from a spermatogonial 

 chromosome, and from that time forward maintains a separate and dis- 

 tinct existence. During the prophases, when occur the profound 

 changes that result in the production of a nucleus with only half the 

 number of ordinary chromosomes, this structure stands aloof and self- 

 contained. With the establishment of the mitotic tigurc of the tirst 

 spermatocyte, however, it takes its place with the other chromatic ele- 

 ments and becomes indistinguishable from them henceforth until the 

 spermatids are formed. Here it again becomes distinct and conspic- 

 uous. 



10. All the phenomena incident to the formation of the male ger- 

 minal elements in the AcrididjB speak for the existence and prevalence 

 of a typical series of processes through which all elements pass on 

 their way to the production of the functional spermatozoon. 



VI. — BIBLIOGRAPHY.* 



1. Brauer, A., 1898. Zur Kenntniss der Spermatogenese von As- 

 caris megalocephala. Arch. mikr. Anat., vol. 42. 



2. Carnoy, 1895. La cytodierese chez les Arthropodes, La Cel- 

 lule, vol. 1. 



3. Cholodkovsky, N., 1894. Zur Frage iiber die Anfangsstadien 

 der Spermatogonese bei den Insecten, Zool. Anz., vol. 17. 



4. Hacker, Valetin, 1897. Ueber weitere Uebereinstimmungen 

 •/.wischen den Fortpflanzungsvorgangen der Tiere und Pflanzen, 

 IJiol. Cent., vol. 17. 



5. Henking, H., 1890. Untersuchungen iiber die ersten Entwick- 

 lungsvorgange in den Eiern der Insecten. 2. L^eber Spermato- 

 genese und deren Beziehung zur Eientwicklung bei Pyrrhocoris 

 apterus M., Z. wiss. Zool., vol. 51. 



(). Henking, H., 1892, idem. 3. Specielles und Allgemeines, ibid., 

 vol. 54. 



*I am under great obligations to Prof. W. M. Wheeler for the kindly loan of much litera- 

 ture that I have used. 



I 



