10 THOS. H. MONTGOMERY jr., 



amitotic nuclear division of which he considers that all t^e sub- 

 sequent generations of spermatogonia have been derived. (This 

 cell has subsequently been discussed by Cholodkovsky, Toyama, 

 V. Erlanger and v. la Valette St. George.) 



Vom Rath ('92), Spermatogenesis of Gryllotalpa. The spermato- 

 gonium contains 12 chromosomes. In the prophase of the 1st sper- 

 matocyte the spirem thread becomes longitudinally split for its entire 

 length, and then divides transversely into 6 segments. Then "die 

 Fadenabschnitte verkürzen sich und die Schwesterfäden jedes Doppel- 

 segments verlöthen an ihren freien Enden mit einander (fig. 13 d) und 

 so entstehen im Kern 6 Chromatinringe, von denen jeder 4 Faden- 

 stücken oder 4 Chromosomen homolog ist". In the next stage each 

 of the 4 rings appears in the form of 4 spherical chromosomes, 

 connected together by linin threads. The latter elements occupy the 

 corners of an imaginary square. "Die Zahl der Chromosomen ist 

 folglich vor der ersten Theilung der Reifeperiode, aber nach der Ruhe- 

 periode von 12 auf 24 verdoppelt." By the 1st division each 2nd 

 spermatocyte receives 2 chromosomes of each tetrad; and by the 

 second division each spermatid receives 1 chromosome from each of 

 the 6 groups of two contained in the 2nd spermatocyte. In these 

 two mitoses no division but only a separation of the chromosomes 

 occurs. In HydropMlus there are 16 chromosomes in the spermato- 

 gonia; the 1st spermatocyte contains 32 chromosomes, "die sich in der 

 Nähe des Aequators in 2 parallelen Kränzen von je 16 anordnen. 

 Jede Tochterzelle erhält 16 ungetheilte Chromosomen, und bei der 

 zweiten Theilung . . . wird die Chromosomenzahl auf 8 herabgesetzt" ; 

 no tetrads are formed. "Bei Dytiscus marginalis . . . konnte ich vor 

 der ersten Reductionstheilung eine Längsspaltung des Chromatinfadens 

 im Knäuelstadium und eine Verdoppelung der Chromosomenzahl 

 schätzungsweise feststellen." 



Vom Rath ('95) presents nearly a literal repetition of his 

 previous observations of Gryllotalpa. He contends against the criti- 

 cism of Rückert ('94, that Vom Rath had failed to give a strict 

 proof of the mode of formation of the tetrads), that the tetrads here 

 are the products of two divisions, and produces a new figure (fig. 6) 

 to bridge over the gap between his previous figs. 13 c and 13 d. 



Wilcox ('95, '94 being a preliminary account) describes briefly 

 the spermatogenesis of Cicada, and more fully that of Caloptenus. 

 Cicada: The spermatogonia are smaller than the 1st spermatocytes, 



