172 BULLETIN OF THE 



the cavity as formerly, and its course is more tortuous, especially in the pos- 

 terior region of the body, than in the preceding. Not only have the temporary 

 cephalic bristles fallen off, but also the long spines found on the body have 

 been replaced by shorter and le.ss conspicuous setas. The most persistent of 

 these deciduous spines are situated in the middle region of the body. In this 

 larva, however, these have given place to minute bristles, and to the " crochet 

 hooks" (Fig. 13, h) of the terminal region. I am inclined to think that the 

 temporary body bristles are confined to that portion of the body -which is 

 described above (Fig. 1, ar) as the anterior region. 



The colors of the oldest larva (Fig. 13) are similar to those of the younger. 

 The prKoral lobe has little color except in the green regions near the eye- 

 spots. There is in the cephalic dorsal walls, in front of each of the lateral 

 eye-spots, a hemispherical green body. Just below and in advance of the 

 median pair of eye-spots there is a body of the same kind, which has a median 

 prolongation extending nearly to the anterior margin of the prasoral lobe. 

 The cephalic tentacles are reddish in color. The lateral lobes on the head, 

 from which the spines formerly arose, are likewise red. The body of the worm 

 is green and brown, with red pigment spots.* 



The temporary cephalic tentacles are homologous with the dorsal cirri, while 

 the temporary sette are strictly the same as those found on the segments of the 

 body. 



It will later be seen, in a description of the young (Ncrinc) Sfio, which like- 

 wise has embryonic spines on the head, that two long dorsal cephalic append- 

 ages or tentacles also exist in this genus. Here likewise these bodies may be 

 regarded as homologous with dorsal cirri, and as belonging to the same segment 

 as the embryonic cephalic spines, which are later dropped. The median and 

 lateral antennas and the palpi are not represented in Prionospio. From this 

 absence of the appendages last mentioned, Ave are not to suppose tiiat they 

 indicate in Lcpidonotus a larger number of cephalic segments than that which 

 exists in Prionosjno. 



In the account given above, the two long appendages to the head are called 

 tentacles, from the fact that in younger larvae they resemble so closely the 

 tentacles of other Annelides, especially those of the Sjoionida. In function, 

 however, they are probably in later larvae branchiae, and ultimately assume a 

 form approximating that of the branchiae in other Annelides. In the growth 

 of the worm, additional branchia; must also be formed, if we are right in our 

 reference of this larva to Prionospio. Intermediate larvae between that last 

 mentioned and the adult may show that a new identification must be made, 

 and that the larva; do not belong to Prionospio. 



* Professor Verrill has kindly examined some of my sketches of this worm, and 

 writes me that they can perhaps be referred to the Annelid which he has mentioned 

 in Amer. Jour., November, }S^2, under tiie name of PrionosjH'o. (See also Trans. 

 Conn. Acad., Vol. IV., PI. XXVIL Fig. 3.) 



