GERM CELLS IN THE ARTHROPOD A 1G7 



An important departure from the usual method 

 of origin of the "Ectosomen" is recorded for Diapto- 

 mus cceruleus. Amma says concerning the process 

 in this species that " whereas in other forms the Ecto- 

 somen first appear during the stage of diakinesis of 

 the first cleavage spindle, in this species they are 

 already present before the pronuclei unite" (Fig. 

 49, H). 



The origin and nature of the Ectosomen are con- 

 sidered by Amma at some length. The hypothesis 

 that these granules arise by the splitting off of parti- 

 cles of chromatin from the chromosomes as occurs in 

 Ascaris is rejected (1) because in one species, Diap- 

 tomus coeruleus (Fig. 49, H), the Ectosomen appear 

 before the nuclear membrane breaks down in prepara- 

 tion for the formation of the first cleavage spindle, 

 and (2) because the Ectosomen do not stain as deeply 

 as chromatin but only slightly darker than the cyto- 

 plasm. The origin of the Aussenkornchen (Ectoso- 

 men) from the nucleolus, as considered probable by 



eine Phasendifferenz, welche in immer starkeren Masse in den hoheren 

 Furchungsteilungen zunimmt (Fig. 49, C). 



"5. Aus dem kornchenfuhrenden Produkte der Kornchenzelle des 

 vierten Teilungsakts, der Stammzelle S, gehen, nachdem diese sich an 

 dem fiinften Furchungsschritte nicht beteiligte, gegen Ende des sechsten, 

 im LX — Zellenstadium, die beiden definitiven Urgeschlechtszellen her- 

 vor ; bei dieser Teilung der S-Ze\\c erscheinen die Ectosomen in ganzen 

 Zellraume (Fig. 49, E, F). 



"6. In Ausnahmefiillen beginnt die S-Zelle sich etwas friiher zu teilen, 

 namlich schon wahrend des Ubergangs des XXX — zum LX — Zellen- 

 stadium. 



"7. Die Urgeschlechtszellen verlieren den Verband mit dem Blasto- 

 derm, sie werden allmahlich in die Tiefe gedriingt (Fig. 49, G)" 

 (pp. 529-530). 



