54 ROBERT H. BOWEN. 



The earliest clear account which I have discovered is that of von 

 la Valette St. George ('86a), who clearly figured the "onion" 

 stage in Blatta (see his Fig. 74), and likened it to a ball of thread. 

 Later, he described much the same appearance in Phratora ( 5 86fr) 

 and (doubtfully) in Forficula ('87). These accounts were the 

 forerunner of a long series of similar observations in which the 

 distinctive feature of nebenkern structure is a more or less thread- 

 like appearance, or more correctly, a division of its substance 

 into layers which are often likened to those of a hemi-sected 

 onion. Another characteristic appearance, occurring often times 

 in conjunction with the preceding, was first described by Plainer 

 ('89), who noted the differentiation of the nebenkern in Lepidop- 

 tera into two substances concentrically arranged an inner, 

 darkly stained core enclosed in an outer clear, non-staining ma- 

 terial. Subsequent observers have found in many forms a similar 

 peripheral zone, often broken up into vacuoles by thin partitions 

 traversing the clear substance. Still a third type of pattern has 

 been described particularly by Holmgren ('02) in Silpha, and by 

 Vejdovsky ('12) in Diestrammena, consisting of a series of 

 smooth or beaded cords running lengthwise through the neben- 

 kern as it begins its elongation. This appearance seems to have 

 been seen by comparatively few observers, and to have been mis- 

 interpreted by all. The problem is, therefore, a twofold one : 

 (i) what is the structural basis of these patterns? and (2) what 

 is the relation of these various appearances to each other and to 

 the course of sperm formation as a whole ? In the account which 

 follows, I have tried to give at least a descriptive answer to these 

 questions. 



The material for this " Study," as in the preceding ones, has 

 been drawn from Hemiptera belonging to the Family Pcntato- 

 inid(z. As I have already pointed out (Bowen, '20), this particu- 

 lar family is characterized by the occurrence of numerous species 

 in which certain of the spermatocytes and spermatids are unusu- 

 ally large as compared with the remaining ones, which are 

 strikingly smaller ("normal") in size. The occurrence of these 

 large spermatids, with correspondingly large nebenkerns, has 

 made possible a structural analysis of the nebenkern which 



