622 ROBERT H. BOWEN 



kern ' patterns ' might follow either a ' spireme ' type or 

 a ' plate-work ' type. As a result of the studies here recorded, 

 however, I no longer tind myself able to accept tlie reality of 

 the ' spireme ', and I now believe that the evidence is indica- 

 tive of a plate-work in th(^ lepido])teran nebenkern essentially 

 like that which I found in fhe Pentatomidae. Indeed, 

 it appears quite likely that the ' spiremes ' sporadically figured 

 by other workers and referred to in my previous paper are all 

 to ho accounted for on similar grounds and to be equally 

 explicable on the basis of their plate-work structure. A 

 plate -work seems to be the fundamental structure of the 

 chromophilic suljstance in the nebenkerns of all insects. 



In this connexion the results of Doncaster and Cannon 

 (1920) on the louse are of special interest. These workers have 

 employed modern technique, and have reached a conclusion 

 which is in accord with my own interpretation of the vesicular 

 nature of the early ne])enkern. Their account is characterized 

 by the remarkaljle conclusion that the nebenkern is formed and 

 goes through the earlier condensation stages in the primary 

 spermatocyte. In the single and abnormal maturation 

 division it passes bodily into the functional spermatid, and is 

 thus already well along in its evolution when sperm formation 

 proper is just beginning. 



Finally, one point in Platner's (1889) old description of 

 Pygaera suggests interesting matter for comparison. I have 

 long been puzzled by this author's small mitosome, 

 which was thus designated because of its supposed relation to 

 a part of the spindle fibres. It is clear now that what Platner 

 really saw was the acrosomal granule, and his account 

 of its elongation, occurring at first in a posterior direction, is 

 remarkably suggestive of my own observations. It is evident 

 from his figures, that the small mitosome was not intensely 

 stained b}' his technique, and his failure to make out the final 

 fate of the ' small mitosome ' (acrosome) is probabh' to be 

 ascribed to the increasing difticulty of demonstrating it as its 

 form became less compact. Gatenby's revival of the term as 

 the micromitosome, for a cytoplasmic granule somewhat 



