262 Miscellaneous. 



there is not, in the neighbourhood of tlie anus, any aperture be- 

 longing either to the cavity of the body or to the aquiferous system. 

 The water rejected by the anal tube is therefore derived from the 

 digestive apparatus. The intestine, stuffed with sand and of ex- 

 treme thinness, contains tolerably powerful muscular fibres at its 

 anterior part, but which gradually diminish towards the posterior 

 part : I believe that the expulsion of the sand cannot be ascribed 

 solely to these fibres, and that aft important part belongs to the 

 organ discovered by Hoffmann, and called by him the " twisted 

 organ " (r/ewundenes Organ). This organ acts as a canal of deriva- 

 tion : it receives the water contained in the sand of the anterior in- 

 testine ; then by the play of the buccal membrane, and the con- 

 traction of the muscles of the first part of the digestive tube, it carries 

 this M^ater into the terminal portion of the apparatus, where it drives 

 before it and carries out the materials accumulated in the posterior 

 intestine. Thus would be explained the anal current and the slow 

 rejection of the sand absorbed ; we also understand why no twisted 

 cast is produced, as in Areiiicola. 



The cavity in which the Echhiocardium is lodged is lined with a 

 glutinous secretion, which was observed by Dr. K-obertsou. On 

 carefully removing the urchin we almost constantly find, in the 

 sandy gangue cemented by this mucus, three or four small crus- 

 taceans, the external aspect of which at once reminds one of the 

 Ilypericp, the usual commensals of Rluzostoma Cuvieri. A more 

 careful examination soon led me to see that these crustaceans belong 

 to the genus Urothoe of Dana, and very probably even to the British 

 species described by Spence Bate under the name of U. mariuvs, the 

 differences relating to perfectly secondary characters, and being at- 

 tributable to less perfect observations than mine. I must, however, 

 indicate one important peculiarity that has escaped the learned 

 authors of the ' History of British Sessile-eyed Crustacea," namely 

 that Urotlwi' marinus presents a strongly marked sexual dimorphism. 

 The most striking character of the male sex is the length of the in- 

 ferior antennse, which greatly exceed the superior ones. It is well 

 known that it is a character of the same kind that distinguishes the 

 male Hyper'ur, (Lest ri (/onus) from their females. This peculiarity, 

 combined with several other analogies derived from their anatomi- 

 cal investigation, snpports the prevision of Westwood, who, from 

 the researches of Hpence Bate upon the development of certain 

 Hyperinao, was inclined to think that a more intimate connexion 

 might perhaps be established between these animals and the sub- 

 family rhoxides, to which Urothoe belongs. 



Among the species of the genus Urothoe figured by Spence Bate 

 some present rather short inferior antennoe ; in the others, on the 

 contrarj', these same organs are of considerable length. With most 

 of these species the descriptions have been drawn up from a very 

 small number of specimens ; we may therefore presume that the 

 differences just mentioned are mere sexual characters, and that one 

 sex only has been described for each of the known types. If we 

 accept this opinion, Urothoe Baird'ii and Urothoe elegans must be 

 regarded ns representing male individuals; whilst Urothoe hrevicor- 

 cornis and Urothoe iDarinvs: are, on tlie contrary, figured from the 



