A Cytologica Study of the Semi-parasitic Copepod, Hersilia apodifr)rmis etc. 425 



cj^tologists first considered tliese phenomena. To say that there is a 

 pseudo-reduction of tlie chromosomes^) of the primary oöcyte or sperma- 

 tocyte, brought about by the segmentation of a spireme into half the 

 normal iiumber of bands, is wholly incomprehensible in the modern light 

 of gametogenesis. None of the recent investigators have shown that 

 such a spireme is ever formed in the production of the spermatocytes 

 or oöcytes. In Hersilia it has been demonstrated that there is a definite 

 series of stages leading up to the formation of double chromatin bands 

 in reduced number. The Icptotene threads gradually evolve from the 

 network following the ultimatc spermatogonial mitosis; these become 

 regularly oriented toward the positive pole of the nucleus in the leptotene 

 bouquet stage. Following is the period of conjugation and the production 

 of the double threads of reduced number which soon become oriented 

 as the zygotene bouquet. That the seriation of the stages is topo- 

 graphical in the testis of the Copepods eliminates the objections 

 which the opponents of parasyndesis have so often made, — namely, 

 that the seriation was a product of the author's mind and did not 

 necessarily exist in nature. In the very first work on Copepod sper- 

 matogenesis, that of Ishikaw^a ('91, Figs. 1—22), with a magnification 

 of only 850 diameters, we find practically a perfect seriation in the 

 stages figured. Haecker ('02) remarks as to the schematic seriation^) 

 of the stages as found in the testis of Heterocope. Hersilia is an object 

 even more favorable that Heterocope, on account of the form of the 

 testis, a long narrow tube. 



On the other hand, the early stages in the growth period of the 

 spermatocytes and oöcytes of the Copepods do not generally allow of 

 good fixation, there being usually considerable shrinkage of the chromatin. 

 It is to be regretted that the Schreiners ('06a, '09b) have never pub- 



1) Matscheck, p. 99): »Die wirkliche numerische Reduktion der Chromosomen 

 erfolgt, wie ich mit Rückert, Haecker imd vom.Rath annehmen möchte, bei den 

 Copepoden dmxh unvollkommene Segmentiermig des ClKomatiniadens, indem der 

 letzte Querteilungsprozeß unterbleibt oder nicht ganz durchgeführt wird und so zwei- 

 wertige oder bivalente Segmente entstehen (Pseudoreduktion, Rückert; Schein- 

 reduktion, Haecker). « 



2) Haecker ('02, p. 30): »Ich glaube sagen zu dürfen, daß die im Beginn der 

 Fortpflanzung stehenden Hekrocope-Wännchen, wie sie im Titisee hauptsächlich im 

 Juni erbeutet werden, mu' hinter wenigen andern Objekten zm'ückstehen düj-ften, was 

 den einfachen und übersichtlichen Bau der Hoden, die geradezu schematische Auf- 

 einanderfolge der Stadien und die Größe und Schönheit der Kernteikmgsbilder an- 

 belangt. « 



