DEVELOPMENT OF ACANTHODRILUS MUILTIPORUS. 511 
Wilson at all like the larval sense-organ of Acanthodrilus, 
and therefore feel almost certain that it does not exist in the 
worms investigated by those authors. 
A sense-organ of this or any kind does not seem likely to 
be of the least use to any embryo which undergoes direct 
development within a cocoon, and is not hatched until mature. 
At the same time Wilson has described in the embryo of 
Allolobophora feetida a structure which may, he thinks, 
have a sensory function. The veutral lip of the stomodeum 
in that worm becomes expanded and thickened, and is consti- 
tuted by a mass of elongate fusiform cells, which is strikingly 
like a taste bud. This body is compared to the larval sense- 
organs of Clepsine. As it is found in A. fetida only, and 
not in L. communis and L. terrestris, where its presence 
is correlated with a tough and jelly-like albumen filling the 
cocoon, Wilson thinks that the group of cells in question plays 
a part in the digestion before absorption of this albumen; it is 
difficult, he thinks, to understand the presence of a sense- 
organ so highly developed in one worm and its absence from 
closely allied forms. ‘This structure is figured (15, fig. 82) by 
Wilson and also by Vejdovsky (1, pl. xv, fig. 5) for the same 
species. In any case the position of this sense-organ or 
glandular organ is totally different from that of the larval 
sense-organ of Acanthodrilus; the one is ventral, the other 
dorsal. The sense-organ of Acanthodrilus can hardly be a 
digestive organ of any kind. Whatever it is, it is transitory ; 
I could find no trace of itin later stages. Ido not think, how- 
ever, that it is of any use to the larva; it is difficult to under- 
stand that any sense-organ could be, which appears and 
disappears at so early a period in the development of the 
embryo. This sense-organ appears to me to be com- 
parable to the larval sense-organ of the Chetopod 
larva and of other worm larve. Such larval sense-organs, as 
is well known, occur in many free-swimming larve ; they are 
not limited to the Chetopoda Polycheta; the Pilidium of 
Nemertes, for example, possesses such an organ. There is 
therefore no need, supposing that my comparison be justified, 
