165 



has been observed as being characteristic throughout adult forms as 

 well, by Hatschek and Fraipont in Polygordius and Protodrilus, by 

 Spengel in Eufiice, and by Pruvot in Syllids in general. The signi- 

 ficance of this relationship of nerve and hypodermal cells was looked 

 upon by Hatschek and Fraipont as indicating a primitive condition. 

 The study of the nerve system in Eunice by Spengel, and subsequent 

 descriptions of the nerve system in Syllidae by Pruvot and Mala- 

 quin, seems to indicate that this is doubtful, since it occurs in higher 

 and lower forms alike. 



In all the Syllidae observed thus far , the relation of the nerve 

 system and hypodermis is described as being very close, the diiferen- 

 tiation of ganglion and hypodermal cells in the head being impossible, 

 while the arrangement along the ventral cord is equally obscure. This 

 I have been able to confirm in several species of Autolytus I have stu- 

 died, and in which I have been equally unsuccessful in distinguishing 

 the two kinds of cells. In these, as in all other Syllids yet described, 

 the head seems to be composed of ganglion cells entirely, so far at 

 least as success at differentiation has been of avail thus far, and it is 

 impossible to distinguish a hypodermal covering overlying these cells. 

 Similarly along the ventral cord, the ganglion cells lie in such close 

 apposition to the hypodermis that a clear dift'erentiation appears to be 

 impossible. Particularly is this the case not only in young and in the 

 posterior part of older specimens, but even in the anterior segments of 

 large and well matured specimens, the nerve cord remains so close to 

 the ventral hypodermis , and the cells of the latter and of the ganglia 

 are so intimately associated, that no satisfactory differentiation can be 

 made. 



In this connection I have studied two species of Proceraea , or- 

 nata and tardiyrada ^ and have discovered in these forms a condition 

 somewhat different from that observed in Autolytus. In these Syllids 

 the mucous glands are very abundant, particularly in the ventral re- 

 gion; and in the ventral hypodermis between the parapodia they form 

 masses that extend some distance into the coelomic cavity. In the 

 region of the ventral cord these glandular structures crowd in between 

 the ganglion cells and the cells of the hypodermis in svich abundance 

 in some segments or parts of segments in the anterior half of the body 

 of the animal, that the two tissues become distinctly separated and 

 their differentiation in such regions is made possible. 



The accompanying figure represents one of the most favorable 

 sections through a ventral ganglion in an anterior segment of Proce- 

 raea ornata. The ganglion with all the cells belonging to it [g. c. and 

 g. c .) have been lifted considerably above the hypodermis by the large 



