50 



the fat-body, on account of its intimate relations with 

 the hyperdermis, is an ectodermal product. This 

 evidence, however, does not seem sufficient to justify that 

 conclusion. 



12. The Reproductive System. 



The Male Organs. — The testes consist of a pair 

 of organs disposed along- the ventro-lateral region of the 

 body, and lying for a considerable portion of their length 

 in close apposition to the mid-gut. Each testis is an 

 elongated chamber, which tapers anteriorly into a delicate 

 filamentous prolongation (Plate YL, fig. 54), and the 

 extremity of the latter is attached to the excretory tissue 

 lying in the mesothoracic segment. Posteriorly, in the 

 region of the second and third abdominal segments, the 

 calibre of the testis increases very considerably, and the 

 mature organ occupies a large portion of the body-cavity 

 in those segments. The hinder fourth of each testis lies 

 completely ventral to the alimentary canal, but as each 

 gland passes anteriorly it gradually comes to lie ventro- 

 laterally in relation to the latter, and finally in its 

 terminal fourth it is completely lateral. In the fifth 

 abdominal segment each testis gives off a short eiferent 

 duct which, uniting with its fellow to form a common 

 canal, opens to the exterior on a small papilla situated in 

 the median line near to the posterior margin of the 

 segment (fig. 54). 



Each testis is in the form of a tube, and its walls 

 consist of a cellular layer containing scattered oval nuclei, 

 but without any cell-boundaries. Externally it is 

 invested by a coat of connective tissue (fig. 59). The vasa 

 deferentia are similar in their structure to the testis wall, 

 and appear to be tubular evaginations of the latter. The 

 median canal, or ductus ejaculatorius (Plate III., fig. 32), 



