No. 446.] PHOTINUS MARGINELLL S. 



three forms of cells are of the same origin 

 tural differences are due to difference in fi 

 Wielowiejski, from his work on Lajiipyn 

 in the possible transformation of the par 

 ventral layer into the cells of the dorsal la\ 

 ological effects of photogeny. iMiierx did ii 

 and after his study of Luciola and two 

 I>ampyriclae, Wielowiejski himself ('89) st 

 forms at least, it was untenable. 



The conditions in Photinus are such as t 

 -such an hypothesis. The two layers are 

 all preparations and the relative thickness ( 

 constant. There is no indication of a trans 

 layers, nor is there any apparent difference in the thic 

 the layers in material put up in early 5 

 at the close of the flying season. Still more important are the 

 inherent differences in the two layers. In the dorsal layer there 

 is a solid mass of polygonal cells, similar in form and size, and 

 irregularly penetrated by tracheae. In the ventral layer there is 

 a distinct division into two elements, the cylinders enclosing the 

 tracheal trees, and the parenchyma cells. The arrangement and 

 distribution of the tracheae of the ventral layer is strikingly reg- 

 ular. The parenchvma cells are extremely irregular, both in 

 form and size. It would, therefore, seem difficult to suppose 

 ver could LU-ow at the expense of the xenlral 



and in that take 



that the 

 laver. 



ve been offered 



the 



I^hotogenic tissue. Kollike 



however, is that the photogenic tissue is ditte 

 This is upheld by a general similarit)- in stru 



