MUSEUM OF COMrARATIVE ZOOLOGY. 175 



already spoken of in 5^310. There is no -well-defined ciliated cephalic ridge 

 bounding the 'jn-aioral lobe. The body is divided into two segments by a deep 

 constriction just in advance of the first of the two bauds 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 setae, 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 setse 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 nc^, raised from the last, but has so many resem- 

 blances to it that it seems identical with the larvse already described. 



The head has the same general form as that of the preceding, although the 

 prseoral 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 

 Avhich 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 (PI. 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 seta, 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 setse 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 larvse which are referred to Aricidea is of interest 

 on account of the fact that the worm has in the oldest larvce the long pro- 



