KEÄIARKABLE SPECIES OF ECIIIUKOIDS. 45 



the latter. In tlu' course tlie single iil)cr.s somewhat diverge 

 from one another ; and after penetrating through the ventro- 

 lateral mesenchymal band ( + ) spoken of before, they finally 

 terminate under the thickened epidermis of the region. The 

 system has certainly greatly to do with the incessant movements 

 exhibited by proboscidial margins of the living worm. 



With respect to the nerves, I have nothing to add to what 

 has been already known from other Echiuroids. Suffice it to 

 say that there exists a pair of strong longitudinal nerves, the 

 lateral nerves (fig. 43, l.n.), which join together near the apex of 

 the proboscis, and that these lateral nerves at intervals of their 

 course give off branches {n.) towards the sides. The branches 

 again split into finer branches, which finally become lost from 

 view in the subdermal tissues. 



Of the blood-vessels, there are three, exactly as known from 

 other Echiuroids. They are one median and two lateral ves- 

 sels, all which, running longitudinally, become finally continuous 

 with one another near the apex of the proboscis. As usual, 

 the median vessel lies imbedded in the mesenchyme, while the 

 thin-walled lateral vessel is contained within a continuation of 

 the body-cavity, the so-called perihœmal cavity (fig. 43, pej'.c). 



The perihsemal cavity represents a moderately wide tubular 

 space, running ventral to the lateral nerve. It is internally 

 lined with the peritoneum consisting of somewhat flattened and 

 stellate cells (fig. 46, pr.). Basally to the peritoneum is a very 

 thin layer of circularly and longitudinally running muscle fibers. 

 Now, the lateral vessel does not lie quite free in the perihiemal 

 cavity, but is attached all along its dorsal line to the wall of 

 the latter (fig. 46, x). Two flat epithelia [ep. and e?it.) of quite 

 similar appearance and an interposed thin layer of muscular 



