88 PROCEEDINGS OF THE ACADEMY OF [Feb., 



In the embryo of Dinophilus, the "trochoblasts," the cells which pre- 

 sumably form this ring, are last seen as a long band, continuous across 

 the ventral surface, but interrupted dorsally by a wide gap. A similar 

 gap is also present in the prototroch of some annelid larvae, as, for 

 example, in Amphitrite (Mead, 1897), and due to the same cause as in 

 Dinophilus, namely, the large size of 2d (X), "the first somatoblast" 

 of von Wistinghausen (1891), and the rapid growth of its dorsal pro- 

 ducts. This dorsal gap is eventually closed in the case of Amphitrite, 

 but it is in this form much narrower than in Dinophilus; the cells com- 

 posing the prototroch are relatively large, and soon become functional. 

 It appears quite probable, therefore, that the dorsal gap seen in the 

 second cephalic band of the mature Dinophilus is ultimately traceable 

 to the peculiar size-relation and growth processes of the cleavage cells of 

 the ovum of this species. 



Just behind the second cephalic band is a pair of shallow grooves, 

 which arise high up on the sides of the head and pass ventrad, widening 

 and deepening slightly, to join the mouth at its lateral margins. These 

 grooves are lined with short cilia throughout their extent. These are 

 the " Wimpergruben" observed by Schmidt (1848) in D. vorticoides, by 

 Hallez (1879) in D. metameroides, and by Korschelt (1882) in D. 

 apatris. They are supposed by the authors mentioned to function as 

 sense organs, but their relation to the mouth seems to indicate that 

 they may also act as food-gathering organs, creating currents which 

 sweep the food particles down into the mouth. It may be remarked in 

 passing that the " Wimpergruben" of this species of Dinophilus are 

 strikingly similar to the ciliated grooves of jElosoma tenebrarum, as 

 described by Miss Brace (1901). 



The seven ciliated bands of the trunk are simple narrow transverse 

 circlets, uninterrupted on the dorsal surface, with the exception of the 

 last. Below they merge wdth the ventral ciliated strip. Each band 

 encircles the middle of its respective segment. The terminal or circum- 

 anal ring is scarcely worthy of the name, since it consists only of 

 two short ciliated bands. These arise at edges of the ventral ciliated 

 area, at the point where the last Segment joins the caudal appendage, 

 and pass upward on the posterior edges of the segment for a short dis- 

 tance (see text fig. I). 



In common with other species of this group, D. conklini possesses 

 conspicuous sense hairs on the anterior surface of the head. Two of 

 these are of considerable size and symmetrically placed, pointing for- 

 ward and slightly outward, while scattered between and around them 

 are a number of smaller hairs. These are in fact tapering projections 



