220 ARTHUE B, SHIPLEY. 



has in some cases been seen to exude from the pores of the 

 glands. 



The external circular layer of muscles is well developed in 

 the introvert, and in the anterior half of the body ; but about 

 the middle of the body it fades away, so that the posterior end 

 is provided only with longitudinal muscles (fig. 7). The cir- 

 cular muscles are arranged in bundles, but the longitudinal 

 are in a continuous sheet. 



Both the cutis and the external and internal layers of 

 muscles take part in the thickening of the skin which exists 

 at the junction of the proboscis and the body. 



The body-wall is lined by an endothelium, which extends over 

 the internal organs. In the living specimens, according to 

 Koren and Danielssen, it can be distinctly seen that this endo- 

 thelium is ciliated, and that the cilia, by their action, keep 

 the perivisceral fluid in motion. 



The General Anatomy. 



If a longitudinal incision be made in the body-wall of 

 Onchnesoma, and the sides reflected, the arrangement of the 

 internal organs and their relation to one another become at 

 once evident without further dissecting. These relations are 

 clearly shown in fig. 3, which I have borrowed from Koren 

 and Danielssen's ' Fauna Littoralis Norvegise.' It will be 

 seen that the oesophagus is very long and loosely coiled, in 

 order to allow for the extension of the introvert. The intestine, 

 whose diameter is larger than the CESophagus or rectum, is 

 also much coiled. The anus is situated rather too far forward 

 to the right of the ventral nerve-cord. 



There is only a single retractor muscle, which has its origin 

 at the extreme posterior end of the body, where the skin is 

 thickened and produced into a blunt point (fig. 7). The other 

 end of this muscle is inserted into the wall of the oesophagus 

 immediately below the brain. The muscle-fibres which com- 

 pose this retractor muscle are bigger than those of the mus- 

 cular sheaths in the skin. They are fusiform, with a rather 

 flattened transverse section and a faint longitudinal striation. 



