170 BULLETIN OF THE 



growth becomes spiniferous. The terminal segments bear small papillae, and 

 are colored with crimson pigment. 



The next following larvae (Figs. 6, 7, 8, 9), which are slightly more mature 

 than the last, differ from it in several particulars. The most important 

 changes which have taken place in the form of the head (Fig. 9) are an antero- 

 posterior lengthening of the whole segment of which it is formed, and a still 

 greater projection of the prseoral lobe, which also becomes more pointed. 

 Perhaps the most significant of the general changes which have occurred is 

 the api^earance of a basal joint in the cephalic tentacles. These appendages, 

 which in all the younger larvae are almost uniform in size throughout, in this 

 are found to be marked at a short distance (b /) from their origin with patches 

 of red pigment. The color is first seen on the anterior wall of the appendage. 

 The walls of the tentacle, where this pigment first appears, are somewhat thick- 

 ened, and a slight corrugation forms on the tentacle at this point (Fig. 9). 



The body of the larva has meanwhile become more elongated, and two addi- 

 tional bundles of setffi have arisen on each side in the anterior or transparent 

 region of the body. The backward growth, leading to an increase in the dis- 

 tance between the " glands " (g) found at the posterior part of the head and 

 the cephalic tentacles, has greatly increased, while the size of the " glands " has 

 diminished. The portion of the intestinal tract which lies in the transparent 

 anterior region of the body, between the glands mentioned above and the first of 

 the four segments which compose the middle body region, fills most of the body 

 cavity, and lies on the dorsal side. Each parapodium of the anterior body re- 

 gion is double, consisting of a dorsal and ventral protuberance, both bearing a 

 small bundle of setoe. The parapodia of tlie middle and posterior regions 

 have a single protuberance of similar character. 



The general appearance of a larva a little older (Figs. 10, 11) than the last is 

 somewhat different by reason of the loss of the temporary embryonic seta (s) 

 formerly found on the head. It is extremely difficult to indicate definitely 

 the time when these bristles normally disappear, but it is probable that the 

 disappearance takes jilace when the larva is in about the condition figured 

 in Fig. 11. The internal modifications of structure which have taken place 

 in passing into this larva are important. The diverticula (" glands," g) 

 mentioned above have changed their position relatively to the crimson pig- 

 ment spots (??is) of the fourth pair of bristles. They are now situated in 

 the same segment as these spots, and a diameter connecting opposite clusters 

 of setae passes through them both. Important changes have also taken 

 place in the cephalic appendages. The basal portion (b f) of the tentacle 

 has enlarged at the expense of the distal, which is the remnant of the em- 

 bryonic appendage. Fully one half of the old tentacle (/) now enters into 

 the formation of the new liasal joint, which ultimately becomes a perma- 

 nent cephalic a]ipendage. The distal end of the same is not changed from 

 the condition which it formerly had. The corrugations of the anterior wall 

 of the basal jt»int have risen into small appendages, which gradually in- 

 crease in size as one compares those found near the head with those at the 



