No. 2.] MORPHOLOGY OF THE ACTINOZOA. 133 



before the publication of the contributions of the Hertvvigs and 

 of von Heider. It adds nothing to Haime's description of the 

 general structure, and falls much behind the Hertwigs' contri- 

 bution in the treatment of the histology. 



In 1888 a paper by C. Vogt ('88) was published, in which 

 was confirmed the supposition of the Hertwigs that new mesen- 

 teries are formed in Cerianthus solely at the dorsal surface, in 

 the region which corresponds in other orders of Actiniaria to 

 the intra-mesenterial space bounded by the dorsal directives. 

 Vogt also calls attention to the unpaired tentacle corresponding 

 to the ventral intra-mesenterial space, which had previously been 

 observed by Haime in Cerianthus and by A. Agassiz ('62) in 

 Arac/mactis, and demonstrated the close relationship existing 

 between these two genera. 



Later in the same year, H. V. Wilson ('88) added to Vogt's 

 observations by showing a similar method of formation of new 

 mesenteries in a free-swimming larva of an unidentified species 

 of CeriantJms obtained at Nassau, Bahama Islands, W.I. 



In the following year Fischer ('89) ^ again called attention to 

 the unpaired ventral tentacle, and to the bilateral symmetry of 

 C. nicmbranacetis. 



Up to this time no accounts of the internal structure of any 

 other species of Cerianthus had been given. The Hertwigs 

 state that they studied C solitarius, but make no special state- 

 ments concerning its general structure. In 1889, however, 

 Danielssen ('89) published an account of the structure of a 

 Norwegian Cerianthus, which he termed C borealis^ and which 

 presents many important variations from the structure of C. 

 membra7iaceus. The principal anatomical peculiarities are the 

 small number of mesenteries, sixteen only, the occurrence of 

 either ova or spermatozoa only in any individual, and the differ- 

 ence in the arrangement of the mesenteries in the males and 

 females, all the mesenteries in the latter extending to the 

 terminal pore, except the ventral directives, which stop a short 

 distance above it, while in the males the arrangement is much 

 more similar to what is found in C membranaceus. 



1 The original paper I have not seen; my knowledge of its contents is derived 

 from the abstract in the Journal of the Royal Microscopical Society, December, 1889. 



2 It seems probable that this form, which Danielssen holds to be distinct from 

 C. Lloydii, is not the same as Verrill's C. borealis, described in 1873. In this case 

 Verrill's application of the name has the priority, as Danielssen's description was not 

 published until 1877. 



