MUSEUM OF COMPARATIVE ZOOLOGY. 171 



distal end of the joint near its articulation with the distal article. These 

 appendages cease at the point of division between the basal and terminal joints. 

 Patches of reddish pigment are found at intervals corresponding with the 

 positions of the parapodia along the anterior region of the body. Although 

 their color is less conspicuous on other segments than on the fourth, it is 

 as a general thing best marked on the anterior somites. The protuberances 

 (" auricles ") from which the embryonic spines (s) of the head formerly arose, 

 are also marked with crimson (Figs. 10, 11). 



In this stage, the peculiar crochet spines (c h) hanging to the posterior region 

 of the body first appear.* On each segment three pairs of these bodies were 

 counted. They arise from the dorsal region of the parapodium. In addition 

 to these appendages the posterior body segments also bear on a ventral eleva- 

 tion smooth spines similar to those on the anterior and middle regions of the 

 body. Later, the hook-like setae (Fig. 13, h) appear on the segments of the 

 middle body region, and rudiments of them may exist in the middle division 

 of the body of the larva we are considering. 



The last segment of the posterior region of the body (Fig. 12, a) has an oval 

 elongated shape, and is dark red in color. It is flattened ventro-dorsaUy, 

 broadening into small lateral expansions. Minute papillae are found on the 

 terminal segment. The anterior body region is now formed of nine, the 

 middle of five, and the posterior of ten segments. The oldest larva of Prio- 

 nospio which was found (Fig. 13) was raised from the last, and differs from it 

 in many particulars. The prseoral lobe (p I) is much larger and more promi- 

 nent than formerly. The cephalic tentacles have wholly absorbed the embry- 

 onic appendages, whose place they now occupy, appearing as two tentacular 

 bodies with appendages (branchiae ?) on their anterior outer walls. The tenta- 

 cles found on the head in the youngest larva have been wholly absorbed into 

 the proximal joint (b t). The separation between the middle and posterior 

 divisions of the body is not as well marked in the oldest larva as in those 

 which we have already considered. The posterior limits of the anterior divis- 

 ion is easily recognized from its transparency. Although this portion is more 

 transparent, its division into different segments is not as evident as in the 

 middle region. It bears nine bundles of setae, arranged at regular intervals on 

 each side, and we may regard it as made up of nine segments. 



Each parapodium consists of a dorsal and ventral prominence, upon each of 

 which there is a small bimdle of setae. The cluster of crimson (m s) opposite 

 the fourth bundle of spines is still well marked. The " glands," which in 

 earlier larvce were so prominent, have in this very much diminished in size, or 

 completely disappeared. 

 The intestinal canal does not now occupy comparatively so large a part of 



* These spines were first noticed in a larva of this age. They may have escaped 

 observation in earlier larva;. Tiie embryonic spines of all Annelid larvae easily fall 

 ofi" when kept in confinement, and there is no uniformity in the appearance of the 

 larva when they disappear under these conditions. 



