194 F. a. HEATHCOTE. 



exterior by a narrow neck and two lateral recesses opening into 

 the neck and placed ventrally to the main sac parallel with the 

 ventral surface of the head. The section C taken through the 

 median portion of the organ exhibits similar relations, excepting 

 that the median dorsal wall of the sac is projected into the 

 interior in two longitudinal folds which make a partial division 

 of the sac into three portions, two deep, wide lateral pouches, 

 and one deep narrow recess between them. This latter I shall 

 speak of as the median recess. A third section, D, is taken 

 through the hinder part of the organ. Here the lateral 

 recesses and the slit-like opening to the exterior are absent 

 and the two dorsal folds almost completely divide the main 

 sac in three portions. 



It is worthy of note that the effect of the median and lateral 

 recesses is to produce a freely projecting lip or edge on the 

 dorsal and ventral aspects of each pouch. 



The general shape of the interior of the organ is therefore 

 posteriorly that of two pouches projecting into the interior of 

 the head, while between them is a median dorsal recess formed 

 by the folds above described, which constitute the inner walls 

 of the pouches where they approach one another. Anteriorly 

 the division into two pouches is not so perfect, but there are 

 two deep lateral ventral recesses. The slit-like opening to the 

 exterior begins at the anterior end and extends about a third 

 of the length of the whole organ. 



The chitinous exoskeleton is continued into and lines the 

 ■whole organ. It is not, however, of uniform thickness. In the 

 median and lateral recesses and on the folds constituting the 

 lips of the pouches it is smooth, but in the pouches themselves 

 it is thrown into a number of folds and bears a large number 

 of chitinous hairs (fig. 2, h.) which project- into the lumen ot 

 the pouches. The folds form alternate ridges and depressions, 

 so that when looked at from the surface through a microscope 

 the chitinous lining of the pouches has a reticulated appearance 

 (fig. 8). The hairs, whose length is about that of the diameter 

 of each pouch, are of peculiar form (fig. 9). Each consists of 

 a stout elliptical basal portion, the inner end of which is inserted 



