MUSEUM OF COMPARATIVE ZOOLOGY. 175 
already spoken of in Spio. There is no well-defined ciliated cephalic ridge 
bounding the preoral lobe. The body is divided into two segments by a deep 
constriction just in advance of the first of the two bands of body cilia. The 
segment which forms the anterior portion of the body shows a number of an- 
nulations; the posterior part of the body is thickly pigmented in irregular 
patches. The final segment bears laterally a pair of long setz, which extend 
backward beyond the posterior end of the body. The anterior body segment 
seems destitute of lateral spines. Bands of black pigment mark the position 
of the two circles of cilia which accompany the body segments. 
In the next oldest larva, raised from the last, we find that the body has 
become more elongated, and is now marked with two deep constrictions 
. forming three body segments. The anterior of these is crossed by a number 
of lines forming the annulations to which reference has already been made. 
The second bears a pair of lateral setae and a band of pigment. The third body 
segment carries two ciliated rings, each encircled with bands of pigment. That 
portion of the head which is in advance of the irregular patches of pigment 
already mentioned bears a small band of cilia. 
An older larva has a body even more elongated than those already described, 
which is divided into four segments, the first and second of which bear lateral 
spines. Two pairs of ocelli have differentiated themselves from the irregular 
masses of pigment formerly found in the dorsal walls of the head. 
The next oldest larva was not raised from the last, but has so many resem- 
blances to it that it seems identical with the larvz already described. 
The head has the same general form as that of the preceding, although the 
preoral lobe is less prominent. It has four eye-spots. The body is divided 
into fifteen segments, each with lateral spines, and a single terminal segment 
which is destitute of these bodies although richly ciliated. The spines of the 
anterior segments are much longer than those of the following. Almost the 
whole interior of the body is occupied by a stomach, which narrows abruptly 
in the twelfth segment, passing into a tubular uncoiled intestine. The head of 
a larva (Pl. VI. Fig. 10) following the last in age is different from that of its 
predecessor, in possessing a single median antenna (mt). The body of the 
same has fifteen segments, and still retains the embryonic sete, although their 
length has very much diminished. The head bears four eye-spots. The 
cephalic auricles as well as the terminal body segment are still richly ciliated. 
The stomach ends in the neighborhood of the tenth body segment. The intes- 
tine is narrow and straight. 
The loss of the embryonic setz of the head occurs at about this age in the 
growth of the worm, and in a larva of about the same age as the last, having 
still fifteen body segments and a ciliated caudal one, these long spines have 
fallen off, leaving the cephalic “auricles” projecting prominently outward 
back of the head and in advance of the anterior body segment. This is the 
oldest larva of the series which was taken. 
The above history of the larve which are referred to Aricidea is of interest 
on account of the fact that the worm has in the oldest larve the long pro- 
