THE SPERMATOGENESIS OF AGALENA NyEVIA. 



LOUISE B. WALLACE. 

 INTRODUCTION. 



A study of the spermatogenesis of the Araneina offers a field 

 of unusual interest to the investigator not only because of the 

 seemingly aberrant form of the mature sperm cells but also be- 

 cause of the presence of conspicuous accessory chromosomes in 

 many species. One needs only to read over the list of subjects 

 in recent cytological literature to realize how much interest is at 

 present centered upon the development of the germ cells as a 

 whole and especially upon certain chromosomes which behave 

 peculiarly and which are designated by various names-- " chro- 

 mosomes speciaux " (de Sinety), " Chromatin nuceolus " and 

 " heterochromosome ' (Montgomery), "small chromosome" 

 (Paulmier), "accessory chromosome" (McClung), " idiochro- 

 mosome," " macrochromosome " and " microchromosome" (Wil- 

 son). Nearly two decades ago, Henking ('90) in his work upon 

 Pyrrhocoris, discovered and described a chromatin element which 

 took part in only one of the spermatocytic divisions and there- 

 fore caused dimorphism of the spermatozoa but he did not appar- 

 ently see the relation between this element and the chromatin 

 nucleoli of the resting stage nor did he offer any suggestion as to 

 its significance. Since the publication of Henking's work, scores 

 of papers on insect spermatogenesis have appeared but as excel- 

 lent reviews of this literature have already been given more than 

 once, it seems superfluous to review it here. Suffice it to say 

 that it is now a well-established fact that among the Hemiptera, 

 at least, dimorphism of the spermatozoa is the rule and further- 

 more that the dimorphism is due to the unequal distribution of the 

 heterochromosomes or to their being of unequal size. In the 

 myriapods, also, Blackman ('or, '03, '05) has found the same 

 dimorphism of the spermatozoa. 



1 Thesis presented to the faculty of the Graduate School of the University of Penn- 

 sylvania in partial fulfilment of the requirements for the degree of Ph.D. 



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