1902.] NATURAL SCIENCES OF PHILADELPHIA. 291 



the transition from the anterior larger to the posterior smaller por- 

 tion is very gradual. The only break in the uniformity of the 

 wall ])ack to the sphincter is a dorsal longitudinal furrow, bounded 

 by two slightly projecting ridges, which extends from the extreme 

 anterior end of the "mid-gut" to a point opposite the junction of 

 the fifth and sixth thoracic segments. At the anterior end of its 

 posterior third the structure thus presented widens out so that, as 

 Ide (3) says, "it terminates like a spatula." The furrow is due to 

 an infolding of the epithelium along the mid-dorsal line (fig. 3), 

 which then spreads out laterally within the lumen, fitting into or 

 covering the secondary grooves formed by the projecting ridges. 

 Following Conklin (see Sec. vi), I shall call the entire structure, 

 grooves and ridges, the typhlosole. The " mid-gut" is uniform 

 in size from the posterior end of the typhlosole to the region 

 of the fourth abdominal segment. Here it is considerably con- 

 stricted by a strong sphincter muscle pinching off, so to speak, a 

 small posterior portion of the " mid-gut," which has already 

 been spoken of as the post-sphincter, and which moulds the pellets 

 of waste befoi-e they are ejected. The typhlosole and sphincter 

 mark off three convenient subdivisions of the ' * mid-gut ' ' : the 

 anterior, containing the typhlosole and reaching to its posterior end ; 

 the median, from the end of the typhlosole to the sphincter muscle, 

 and the postenor, including that portion covered by the sphincter, 

 and the post-sphincter portion as far as the rectum. 



2. Glands. — Huet (7) has described for Ligia a pair of salivary 

 glands lying on the posterior ventral wall of the oesophagus and 

 opening by an extremely narrow aperture into this portion of the 

 canal. He has demonstrated that they are salivary glands by dis- 

 secting them out in alcohol (which does not destroy diastase) and 

 placmg potato starch in a watery extract. Dextrose was detected 

 after twenty -four hours. Ide (3) considers these glands as cutaneous 

 appendages, disputing their connection with the oesophagus, 

 although admitting that they may be concerned in digestion. On 

 account of their very small size and the uncertainty of their morpho- 

 logical nature, no attention has been given them in this study. 



The only other digestive gland with which we have to do in the 

 isopods is the hepatopancreas. It consists, in the forms studied, 

 of two pairs of blind tubes, placed a pair on each side of I he intes- 

 tine, into which they open, at the anterior end, by a l-shuped 



