Studies in Crustacean Spermatogenesis. 477 



The formation of the chromosomes from the nuclear network 

 occurs in one of two ways, either around prochromosomal centers 

 (Homarus, Hippa, Astacus, Talorchestia), or as more or less elon- 

 gated loops or threads. (Oniscus, Idotea.) Of course these need not 

 ,be considered as entirely distinct methods of formation. Transitions 

 might readily occur between a condition in which there is an early 

 determination of chromatic material towards circumscribed areas and 

 one in which the network first breaks up into loops or strands and 

 is later condensed. 



The parallel conjugation of chromosomes during synapsis seen in 

 Hippa, Homarus and Idotea/ and their subsequent divergence recalls 

 similar phenomena described for such widely different organisms as 

 flowering plants (Bergh, 1904), Xematoda (]\[arcus, 1906), Hex- 

 apoda (Otte, 1906; Stevens, 1906; Henderson, 1907) and Amphibia 

 ( Montogomery, 1903). Multiplication of such instances indicates 

 that this may be the usual method of conjugation during synapsis, 

 although in many cases obscured by the dense massing of the chro- 

 matin at this stage. This method of conjugation of course suggests 

 a more intimate union of male and female components and an attrac- 

 tion between the elements of the chromosomes rather than between 

 the chromosomes as a \yhole. 



The tendency to polarity in the arrangement of the chromatin seen 

 in Idotea, Hippa and Astacus evidently depends on the location of 

 the kinoplasm, whether within or without the nucleus, and as the 

 polarity is accompanied by a centrifugal movement of the chromo- 

 somes as mitosis approaches, it is a tempting hypothesis to suppose 

 that at this period some substance is elaborated in the kinoplasmic 

 region which sets up an outward current and that this current carries 

 the chromosomes with it. 



Relationship clearly does not determine the location of kinoplasm, 

 for it arises within the nucleus in Idotea and without in Oniscus. 

 To a slight degree it seems to determine the appearance and behavior 

 of the nucleoli, but not nearly to the same extent that it affects the 

 origin and arrangement of mitochondria. 



^Somethins similar has been observed for Cyclops streniuis by Lerat (1005). 



