66 MCMURRICH. [Vol. XI. 



Part I. — The Phenomena of Impregnation and the 

 Formation of the Egg-membranes in Jaera. 



I. The process of Impregnation injaei^a. 



On examining a series of transverse sections through an 

 adult female Jaera my attention was arrested by a peculiar 

 chitinous body, circular in section and composed of a series of 

 concentric layers (PI. V, Fig. i, Sp), which occurred on each 

 side of the mid-line, just below the tergum of the fifth thoracic 

 segment, — a short canal, at the bottom of which it lay, running 

 forwards and upwards to open between the fourth and fifth seg- 

 ments. On sectioning other individuals similar structures 

 were found, varying, however, considerably in position, some- 

 times having a more lateral and sometimes a more median posi- 

 tion, sometimes near the dorsum of the body, or at other times 

 seated more deeply and more posteriorly, but always surrounded 

 by a cellular investment. The impression which one obtains 

 from the examination of the relations of these structures in 

 a number of specimens is that they are bodies which are at- 

 tached to the dorsum of the female in the region indicated 

 above, and which gradually migrate downwards and backwards 

 into the body. In other words, they appear to be intrusive 

 bodies, and do not, strictly speaking, belong to the category of 

 female organs. 



Sye ('87) mentions the occurrence of these structures, but 

 has not followed their relations sufficiently to arrive at any 

 conclusion as to their significance. He states, however, that 

 they do not occur in the male, and were found in the female 

 only during the breeding season, not occurring either before 

 or after that period. 



The investigation of this structure does not strictly fall 

 within the scope of the present study, but incidentally some 

 facts regarding it have been discovered which throw some light 

 upon its significance, and may be recorded here in the hope 

 that the attention of other observers will be directed towards 

 a fuller investigation of the subject. 



