MUSEUM OF COMPARATIVE ZOOLOGY. 179 



anterior body region. The stomach (s) fills most of the body cavity from that 

 point to the sixth segment of the posterior region. The intestine (i) is coiled 

 in the posterior part of the body cavity behind the stomach. The anus, as 

 before, opens dorsally. The " tail," a median terminal appendage, is segmented 

 and slightly enlarged at the distal end into a knob or button. 



The oldest larva (Fig. 11) gives no more definite information than others 

 already known in regard to the genus to which it belongs.* The posterior part 

 of the body of this larva is swollen, leaving the band of cilia about midway in 

 its length. The praeoral lobe has become more contracted, and the external 

 surface of the body is covered with small papilla. Another pair of pigment 

 spots — the cephalic eye-spots — has been added to the two already existing. 

 The cephalic appendages have elongated so that their- tips extend downward to 

 the vicinity of the ring of cilia. There are now ten parapodia in the anterior 

 region of the body between the cephalic appendages and the band of cilia. 



The posterior portion of the body is almost hemispherical. The median anal 

 appendage is greatly reduced in size, appearing as a slight projection, on either 

 side of which there are similar lateral knobs. The intestine is slightly coiled, 

 and lies wholly in the posterior body cavity. 



Phyllochaetopterus sp. 



Plate III. 



The youngest larva (Figs. IG, 17), of this genus which we have obtained 

 resembles closely a young Telepsavus. It is mesotrochal, and has a large prse- 

 oral lobe, which, like that of the older form of the same figured by Claparcde 

 and Metschnikofl',f bears six eye-spots upon the dorsal region. These eye-spots 

 consist of a pair of median and two lateral ocelli on each side. The oral lobe 

 carries on its rim, just in advance of the median pair of ocelli, a flagellum, as 

 in Telepsavus. The young Telepsavus has four eye-spots ; the median pair 

 failing even in a larva in which the tentacles have begun to form on the sides 

 of the head. The youngest Phylloclioitoptcrus, even when it has developed into 

 a larva possessing six eye-spots, is still destitute of lateral cephalic tentacles. J 



* Professor VerriU (Trans. Conn. Acad., Vol. IV., PI. XVITT. Figs. 16, 17) fitjnres 

 tliis larva, and in MS. explanation of plates, which he has kindly sent me, refers it 

 doubtfully to Spiochcetopterus. His larva is a little younger than that which is here 

 figured in Fig. 19. 



t Op. cit. 



% The Annelid larva {Mesntrocha spTomhtta) described by Johannes Miiller (Mai- 

 ler's Arcliiv, 184G), by Busch (Ibid., 1847), and by Max Muller (Ibifl., 1855), seems 

 more closely allied to this than to the ])vece'Jilng' (Telepsavus larra). Like the 

 PIti/l/ochrctopterus larva, it has six eye-spots and two mesial rings of cilia separated 

 by a wiile segment. In the figures, however, which are given by the above-men- 

 tioned authors, there is no representation of a tuft of cilia (flagellum) situated on 

 the praeoral lobe between two of these eye-spots, as is mentioned in the larvae of 



