14 AKT. 4.- — I. IKEDA I 



bands stretcliiûg along the bnsnl line of the left retractor, as 

 well as in the corresponding position on the right side. Tlie 

 œsophagus [œ) is connected by a membraneous muscle with the 

 inner side of the left ventral muscle. The dorsal vessel (dv) 

 runs along the entire dorsal side of the oesophagus ; it is not 

 j)rovided with contractile villi. The intestinal convolution [ic) 

 consists of about 30 double spirals around the spindle-muscle 

 {sjii). The latter does not posteriorly pass out of the spirals to 

 insert itself in the body- wall. The small diverticulum attached 

 to the beginning of the rectum is comparatively short. Two 

 fine fixing muscles {ß/i, Fig. 43), are attached to the fourth spiral 

 of the convolution ; they are rooted on the body- wall at points 

 lying just behind the bases of the dorsal retractor muscles. 

 The segmental organs (so), of a deep reddish brown color, are 

 of a moderate size. Their external apertures are situated on the 

 same level as the anus (a). Tentacles are tolerably numerous 

 and encircle the mouth in a ring. No eye-spot can be detected 

 on the ganglion. 



A peculiar reticular structure (r^, Fig. 43) is found lining 

 the inner surface of the body-wall in a zone bounded anteriorly 

 by a line joining the external apertures of the segmental organs 

 and posteriorly by a line running midway between the roots of 

 the dorsal and ventral retractor muscles. It appears as an 

 irregular, small-meshed network of trabecuhe, forming a layer 

 over the region indicated. One small portion of the structure 

 is shown in Fig. 44, as seen in surface view under a low mag- 

 nifying power. Examined on sections, the trabecuhe are seen to 

 be composed of very fine connective-tissue fibers in bundles and 

 of a few muscle-fibers ; further it can be made out that the 

 reticular layer is joined to the body-wall by numerous short 



