292 PROCEEDINGS OF THE ACADEMY OF [^lay, 



aperture. The two tubes ou the same side imite into a transverse 

 canal which joins that of the other side at the aperture. The 

 tubes extend ahiiost the entire length of Ihe body cavity, their 

 tapering blind ends reaching into the abdominal segments (fig. 1). 

 It is to "Weber (37) that we owe the recognition of the mixed na- 

 ture of this gland and the application to it of the name hepato- 

 pancreas, introduced by Krukenburg (24) for the analogous organ 

 of fishes. 



2. Microscopic Structure of Intestine. 



The wall of the " mid -gut," as of the other divisions of the 

 intestine, is made up of four coats which have been recognized by 

 all the later writers. Beginning with the outer or coelomic side, these 

 are the muscular coat, the basement membrane, the epithelium and the 

 intima or cliitinous lining. The muscular coat has been fully de- 

 scribed by Ide (3) and Schouichen (6). It consists of two layers, 

 an outer longitudinal and an inner circular. Over the anterior 

 portion of the " mid-gut " (i. e., as far back as the typhlosole ex- 

 tends) the outer is imposed upon the inner ; posterior to this both 

 layers thin out so that the fibres are quite widely separated from 

 one another, each one running in the groove between adjacent 

 rows of cells. They also fuse together and anastomose freely, so 

 that a muscular network is formed, through the meshes of Avhich 

 the cells project. The sphincter, according to Ide, is an additional 

 layer lying outside the longitudinal and constituting a second circu- 

 lar one. The inner circular layer is very much reduced at this 

 place, so that only a few fibres appear. 



The other coats, as McMurrich has indicated, properly belong to 

 the epithelium. Both the basement membrane and the chitinous 

 lining are formed by the epithelial cells. The former is a smooth 

 membrane of uniform thickness which accommodates itself to all 

 the irregularities of the outer surface, dipping into the dorsal fur- 

 row and keeping closely applied to the cells. We have already men- 

 tioned the very large size of the epithelial cells. As Ide observed, 

 they are often to be seen with the naked eye. They are repre- 

 sented in fig. 1 for Oniscus asellus, 12 mm. long, magnified just ten 

 diameters. Those in the median portion of the ' ' mid-gut ' ' are most 

 easily seen, because only partly covered with muscle. Their ends, 

 projecting freely into the coelome, appear as little mounds on the 



