SPERMATOGENESIS OF AMERICAN CRAYFISH 595 



Prowazek ('02 a) briefly discusses the formation of tetrads 

 in the rhinoceros beetle, in Astacus and a land snail. In Astacus 

 the resting stage of the nucleus shows a finely granular structure. 

 Soon the chromatin aggregates into irregular islands, and from 

 these the chromosomal threads make their appearance. These 

 threads join one behind the other, in pairs, giving rise to 

 the double or paired chromosomes, and appear snake-like or 

 S-shaped. (It becomes evident from this that Prowazek regards 

 the chromosomes in this form to be joined end to end or telo- 

 synaptically) . The paired chromosomes now thicken and a 

 longitudinal split occurs, dividing the paired threads into four, 

 from which the tetrads arise. 



In another article, Prowazek ('02 b) traced the spermato- 

 genesis of Astacus fluviatilis through the maturation divisions, 

 laying particular emphasis on the transformations undergone 

 by the mitochondria through these stages. During July the 

 nurse cells in the tubules were found to divide amitotically, and 

 right next to them, primordial spermatogonial, as well as oogonial 

 cells could be found. Within the nucleus of the spermatogonia, 

 U-shaped chromatin rods were seen, their free ends facing towards 

 the nuclear wall, while inside the cytoplasm an idiozome and a 

 dense mass of mitochondria, lying off at one pole, could be dis- 

 tinguished. 



The oogonial cells were very much larger than the spermat- 

 ogonial cells. They also contained denser zones of cytoplasm 

 surrounding the nucleus, as well as along the periphery of the 

 cell wall. These oogonial cells soon degenerate, while the 

 spermatogonia undergo development and give rise successively 

 to the primary and secondary spermatocytes. 



Between the first and second maturation divisions, no distinct 

 resting stage was found. During these divisions, the mitochon- 

 drial mass becomes scattered through the spindle fibers, and, 

 when cell division occurs, equal portions of it are given to each 

 of the resulting two cells. 



Labbe ('03) in a preliminary paper, discusses the spermato- 

 genesis of Homarus, Palinurus, Galathea, Eupagurus, PorceJlana, 

 Maja, Stenorhynchus, Inachus, Carcinus, Cancer, etc. In these 



