NOTES ON THE ANATOMY OP DINOPHILUS. 121 



vesiculae seminales (in whicli respect, however, B. vorticoides may 

 possibly be found to agree with D. tseniatus) . 



The characters above given appear to be amply sufficient to 

 justify the formation of a new species. The species which most 

 resembles D. tseniatus is probably D. gigas, Weldon, which, however, 

 differs from it in such important features as the number of the seg- 

 ments, the arrangement of the ciliated rings, the general character 

 of the reproductive organs, and more particularly the absence of a 

 copulatory organ in the male sex. 



External Features — The form of the body is shown in PL IX, 

 fig. 1, which represents a rather young individual (the distinctness 

 of the cilia having been somewhat exaggerated) . In an old animal, 

 distended with ripe g-enerative products, the external segmentation 

 is not nearly so conspicuous as in the specimen figured. The 

 arrangement of the cilia is often difficult to make out in living 

 specimens, but may be very easily observed after treatment with 

 hot corrosive sublimate, and before the extraction of the orange 

 pigment by means of alcohol. In specimens thus treated, the cilia 

 appear as white bands running over an orange background ; when 

 seen from the dorsal surface, the two rings of each segment together 

 give rise to the impression that the middle region of the segment is 

 encircled by a broad band ; this appearance has suggested the 

 specific name tseniatus. 



The ciliation of the head is best studied in a sublimate specimen, 

 seen from the anterior pole (fig. 8). The general surface of the 

 head is not ciliated, the cilia occurring, on the contrary, as two de- 

 finite prseoral rings, between which are situated the eyes, near the 

 dorsal surface. The anterior ring is more or less triangular, the 

 apex of the triangle being directed dorsally. 



In looking at the animal from above, it is seen that the posterior 

 cephalic ring passes dorsally across the equator of each of the eyes 

 (fig. 1). This ring, unlike all the other ciliated rings of the animal, 

 is composed of several circlets of cilia. Of these, the first consists of 

 long cilia directed forwards, and the third or last of somewhat 

 shorter, backwardly-directed cilia. Between the two circlets occurs 

 an intermediate series of very minute cilia (figs. 1, 15). It follows 

 from this description that in structure, as in position, the second 

 cephalic ring resembles the prgeoral ciliated band of a Trochosphere 

 larva. No ciliated pits were observed. The head bears long, stiff 

 sense-hairs arranged in two groups, situated within the area circum- 

 scribed by the anterior ciliated ring (fig. 1). Similar sense-hairs 

 occur on various parts of the body and tail. 



The study of longitudinal sections, in which, however, the cilia were 

 not very well preserved, appeared to show that the second pr^oral 



