2 E. W. MACBRIDE. 



"wheels" are few in number and confined to the lateral processes, 1-6 in each, 

 whereas in our larva they are extremely numerous. Numerous " wheels " with 

 13-16 spokes are described by Prof. Chun (2) in a peculiar Auricularia which he 

 fished up at Orotava at the Canary Islands, and which has been named Auricularia 

 nudibranchiata by Dr. Mortensen (8). 



A few words upon the general anatomy of the Auricularia larva may not be 

 out of place here. As all zoologists are aware, it possesses, like other Echinoderm 

 larvae, a thickened band of ciliated ectoderm as locomotor organ, and this band has 

 the form of a folded loop, the longest axis of which is parallel to the long axis of 

 the larva ; in a word, the loop has two long parallel sides and shorter anterior and 

 posterior cross-pieces connecting them. The anterior cross-piece is folded backwards, so 

 as to form a frontal loop surrounding the forehead or " frontal field," whilst the 

 posterior cross-piece is folded forwards so as to surround an " anal field " in which 

 the anus opens. This loop may be termed the anal loop. The adjacent portions of the 

 frontal and anal loops are termed by Dr. Morteusen (" Quersaume "), which we may 

 translate as anterior and posterior " transverse bars." The mouth is situated in a 

 depression between the anterior and posterior bars termed the oral field. The ciliated 

 band, in addition to the re-entrant frontal and anal loops, is produced into a number of 

 " processes " which are homologous with the arms of the Echinopluteus and 

 Ophiopluteus larvae. Of these the prae-oral processes are developed from the 

 sides of the frontal loop ; and the post-oral processes from the sides of the 

 anal loop. Where the frontal loop passes into the sides of the ciliated band, there 

 are developed the antero-dorsal processes. From these same lateral portions of 

 the band are developed further back intermediate-dorsal and postero-dorsal 

 processes. Finally, where the anal loop passes into the lateral portions of the band, 

 we have the postero-lateral processes. These last, in the opinion of Johannes 

 MiAller, showed a resemblance to the human ear, whence the name " Auricularia " 

 was coined to designate the larva. 



We have seen that A. antarctica cannot be identified with the larva of Synapta 

 digitata, since in the latter the " wheels " are few in number and are confined to the 

 processes (1-6 in each). But there are other differences scarcely less striking. In the 

 larva of Synapta digitata the outline of the ciliated band is flowingly sinuous, none of the 

 processes being very strongly marked, whereas in our larva the processes are marked off 

 by deep re-entrant folds and show some secondary plications. Then the spot where the 

 frontal loop passes into the lateral portions of the ciliated band is at the anterior pole 

 in the larva of Synapta digitata, but in our larva it is displaced far back on to the 

 dorsal surface. The oral field is comparatively broad in the larva of Synapta, but in 

 our larva it is reduced to a narrow slit, the anterior transverse bar actually overlapping 

 the posterior bar at the sides. On the other hand our larva resembles the Orotava 

 larva not only in the great number and wide distribution of the " wheels," but in the 

 displacement of the point of union of the lateral part of the ciliated baud with the 



