38 NOTES ON THE ANATOMY OF DINOPHILUS. 



It will not be superfluous to call attention to the fact that the 

 bright orange colour which is so conspicuous a feature of B. tsenia- 

 tus (as of certain other species of JDinophilus) cannot easily be re- 

 garded as a protective colouration. The rock-pools inhabited by 

 this species of Dmophilus contain numerous bright green Algse^ and 

 there is not the slightest difficulty in detecting with the naked eye 

 individuals of D. tseniatus, whether crawling on this green back- 

 ground or on the mud or rocks which occur at the bottom of the 

 tide-pool. 



With regard to the habits of the animal, it may be noted that, 

 so far as I am aware, it never performs those gyrations round a 

 centre formed by the attachment of the tail to a foreign body, which 

 have been described as of frequent occurrence in D. metamer aides, 

 for instance (4). The animal crawls (no doubt by means of its 

 cilia) with considerable rapidity, but it is able to swim freely in the 

 water; the latter method of progression appears to be specially 

 characteristic of young individuals. 



Specific Characters — JJinophilus tseniatus is characterised as follows : 

 Head with two circlets of prseoral cilia. Body composed of five 

 segments and a tail. Segments sharply marked off from one 

 another in young individuals, each encircled by two rings of cilia, 

 incomplete ventrally, where they are interrupted by the uniform 

 ciliation of the ventral surface. Anus placed dorsally to the base 

 of the conical unsegmented tail, surrounded by a ring of cilia, in- 

 complete ventrally. Skin containing large numbers of transparent 

 glandular bodies. Sexes not dimorphic. Maximum length, in either 

 sex, about 2 mm. Colour bright orange, usually brighter in the 

 male than in the female. Testes in the male extending nearly the 

 whole length of the body, on the ventral and lateral sides of the 

 alimentary canal ; spermatozoa very long and undulating. Vesicula 

 seminahs formed by the modification of the fifth nephridum on each 

 side, opening into a median copulatory organ, whose external aper- 

 ture is ventral and slightly posterior to the anus. Ovaries in the 

 female four-lobed. Nephridia ten in number (five pairs), the fifth 

 pair modified as a vesicula seminalis in the male. Ventral nervous 

 system segmented. 



As characters recognisable in living specimens, and which are 

 sufficient to distinguish this species from all others at present known 

 may be mentioned the following : 



(1) The existence of five body-segments (in addition to the tail), 

 each encircled dorsally and laterally by two rings of cilia ; the seg- 

 mentation being sharply marked in immature individuals. 



(2) The four-lobed condition of the ovaries in the female. 



(3) The existence, in the male, of a median penis and of lateral 



