170 BULLETIN OF THE 
growth becomes spiniferous. The terminal segments bear small papille, and 
are colored with crimson pigment. 
The next following larve (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 preoral lobe, which also becomes more pointed. 
Perhaps the most significant of the general changes which have occurred is 
the appearance of a basal joint in the cephalic tentacles. These appendages, 
which in all the younger larvee are almost uniform in size throughout, in this 
are found to be marked at a short distance (b f) from their origin with patches 
of red pigment. The color is first seen on the anterior wall a 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 sete 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 sete. The parapodia of the middle and posterior regions 
have a single protuberance of similar character. 
The general appearance of a larva a little older (Figs. 10, 11) than fhe last is 
somewhat different by reason of the loss of the temporary embryonic sets (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 place 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 (ms) of the fourth pair of bristles. They are now situated in 
the same segment as these spots, and a diameter connecting opposite clusters 
of sete passes through them both. Important changes have also taken 
place in the cephalic appendages. The basal portion (bt) 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 (é) now enters into 
the formation of the new basal joint, which ultimately becomes a perma- 
nent cephalic appendage. 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 joint have risen into small appendages, which gradually in- 
crease in size as one compares those found near the head with those at the 
