1902.] NICHOLS — SPERMATOGENESIS ONISCUS ASELLUS LINN. 95 



1895. Auerbach compares the spermatozoon of Astacus fluviatilis 

 with those of other Crustacea, Insects and Vertebrates, with a view 

 to discovering homologies of head, apex, middle-piece and tail. 

 The cyanophilous, saucer-shaped nucleus corresponds to the head of 

 more highly developed spermatozoa, its pole therefore to the ante- 

 rior end of a flagellate spermatozoon and the surrounding proto- 

 plasm to the sheath of the head. The ''globule achromatique " of 

 Gilson is the anlage of the apex. The " tigelle " of Gilson, which 

 Auerbach found to be erythrophilous, he regards as the anlage of 

 the middle-piece. In the genera Pagurus, Eupagurus, Clibanarius 

 and Ethusa the '' tigelle " is prolonged into what Auerbach regards 

 as a rudimentary tail. The bladder-like vesicle is perhaps a kind of 

 '* Schwanzkappe," possibly comparable with the sheath sometimes 

 surrounding the place of origin of the tail in immature vertebrate 

 spermatozoa. The extremity regarded by Grobben as the head 

 would, according to Auerbach's interpretation, be the tail end. 

 For a more detailed account of the Decapod spermatozoa, of which 

 that of Astacus may be taken as a type, the reader is referred to 

 the works cited above. 



Stomatopoda, Schizopoda, Amphipoda. 



1885. Gilson, in his excellent and very comprehensive work, de- 

 scribes also the spermatozoa of the Stomatopod Squilla, the Schizo- 

 pod Mysis and the Amphipod Gammarus. The whip-like sperma- 

 tozoon of Mysis is strikingly similar in shape to that of the 

 Isopods. That of Gammarus is flagellate and that of Squilla 

 vesicular. 



Isopoda. 



1883. Herrmann studied among the Isopoda, Ligea, Idotea and 

 Sphaeroma. His description is unaccompanied by figures and is 

 difficult to comprehend. The spermatic filaments, he says, are 

 united in numbers varying from eighty to one hundred. The 

 bundles are found lying amongst the cells which line the walls of 

 the tube. He did not find isolated spermatozoa, except in the 

 oviduct of the female, where they retain their habitual form 

 and immobility. The large cell of the vas deferens he con- 

 e-iders as homologues of ovarian cells and calls them ''ovules 

 males." 



1884-1886. Gilson (Oniscus asellus). Groups of six spermatids 



