SPERMATOGENESIS OF AMERICAN CRAYFISH 591 



ular nuclei which are imbedded in a syncitial mass of proto- 

 plasm. These latter are the nurse cells, from which the spermato- 

 gonia are derived, the nurse cells increasing in size, becoming 

 spherical in outline and then being surrounded by a distinct mass 

 of cytoplasm. Grobben says: 



Wir finden also dass zwischen Spermatoblast (English, sperma- 

 togonia) und Ersatzkeim (English, replacement cell) ebensowenig 

 Unterschied besteht, wie zwischen Eizelle und Follikelzelle und die 

 ausserordentliche Aenlichkeit beider Bildungen muss die schon so oft 

 vorgebrachte Ansicht von der Homologie des Hodens und des Ovariums 

 sehr unterstiitzen. Jeder Ersatzkeim ist potentia ein Spermatoblast, 

 jede Follikelzelle potentia ein Ei. Es entstehen die Spermatoblasten 

 durch Umwandlung der Ersatzkeime wie die Eier durch Umwandlung 

 aus den Follikelzellen bilden. 



In 1906, Grobben published a short article on the sperm of 

 Pandalus narwal, Pasiphaea sivado, Nephrops norvegicus, Xantho 

 rivulosus, Homola spinifrons, Portunus corrugatus, Pagurus 

 calidus, Pisa and Scyllarus arctus. The spermatozoa of these 

 species are very briefly described, and then their resemblances 

 are traced with a view toward a systematic classification of the 

 forms; (similar to Koltzoff's work). 



Sabatier ('85, '93) studied the germ cells of many Crustacea 

 including such forms as Astacus fluviatilis, Pagurus striatus, 

 Pagurus calidus, Pagurus angulatus, Paguristes maculatus, 

 Eupagurus lucasi, Diogenes varians, Carcinus maenas, Maja 

 verrucosa, Maja squinado, Palinurus vulgaris, Homarus vul- 

 garis, Scyllarus arctus, Inachus scorpio, Stenorhynchus phal- 

 angium, Dromia vulgaris, Corystes dentatus, Pale^on serratus, 

 Palemon treillanus, Crangon, etc. The species most studied 

 , were Astacus fluviatilis and Pagurus striatus. 



Special attention was paid to the origin of the spermatogonia. 

 The spermatogonia or the 'protospermatoblastes' as they are 

 called by Sabatier, are, according to his account, derived from 

 the replacement layer of cells found in the tubules of the testis, 

 and these, in turn, are derived from the connective tissue layer 

 that forms the skeleton of the tubule. During its early condition 

 of development, the tubule presents the form of a hollow cylinder, 

 whose walls are formed of a layer of connective tissue and some 



