7O ROBERT H. BOWEN. 



beginning of this paper as two characteristic types in the insect 

 nebenkern. It remains now to consider the nature of the third 

 type of pattern the smooth or beaded cords running parallel to 

 the long axis of the nebenkern as mentioned in the paragraph re- 

 ferred to above. This type of pattern has been described espe- 

 cially by Holmgren ('02) and Vejdovsky ('12). Fragmentary 

 references to it occur, however, in a number of other cases, as for 

 example those of Pygccra (Meves ('oo)) and of Notonccta (Pan- 

 tel and de Sinety ('06)); Henneguy ('96) also seems to have 

 figured it crudely in Pyrrhocons, and Boring ('07) shows it very 

 clearly in Pccciloptcra. In so far as any explanation of this pat- 

 tern has been attempted, all accounts agree in connecting it ulti- 

 mately with the preceding patterns, that is, with the chromophilic 

 substance. This is certainly not the correct origin in thePcntato- 

 midcc; in fact, we have here to deal with a structure of entirely inde- 

 pendent (so far as its morphology is concerned) origin. Indeed, 

 it is better to consider this from the standpoint of the evolution of 

 a new substance within the nebenkern, rather than as a mere pat- 

 tern comparable to those which have preceded it. 



This substance;, then, makes its first appearance at a period 

 approximately that of Figs. /, 8 and 9 in other words at about 

 the time when the chromophilic substance first seems not only to 

 be condensing but actually in process of dissolution. This new 

 material appears at this time in the form of vacuoles scattered 

 about in the chromophobic substance between the chromophilic 

 plate-work and the peripheral wall of the nebenkern (Figs. 7, 8 

 and 9). These vacuoles are rather inconspicuous at first, their 

 periphery staining faintly in Benda preparations, though I am 

 not able to say positively whether the alizarin or the crystal violet 

 is responsible for the coloration. It seems to be the former as a 

 rule. The origin of these vacuoles is entirely obscure. Perhaps 

 they are produced as a special differentiation of the chromophobic 

 material. However, the fact that these vacuoles are on the in- 

 crease while the chromophilic material is decreasing suggests 

 that there is possibly some connection between the two processes. 

 It might be supposed that the vacuoles are differentiated out of 

 material derived from the chromophilic mass in some indirect 

 way. 



