No. 3.] PODARKE OBSCURA VERRILL. 435 



" problematic bodies " of Amphitrite. In Nereis, Wilson sup- 

 poses each to arise from a single cell, which becomes vacuolated 

 and probably has a glandular function. In Podarke there are 

 two on a side, closely crowded together just in front of the eye- 

 spot, and a fifth very small one on the median line in front. 

 They stain very deeply with haematoxylin, an outer portion 

 (Wilson's "duct") staining much more deeply than the inner. 

 From the number of nuclei surrounding each "body" in the 

 early stages, I think they are formed from more than one cell. 

 Their staining reactions indicate that they have a glandular 

 function, and they are apparently the only glands in the body. 

 In the case of these glands, as well as in that of the so-called 

 "slime glands" in other annelids, I agree with Eisig (No. 8), 

 that they probably have an excretory rather than a slime secret- 

 ing function, the necessity for the one and not for the other 

 being apparent. 



A marked feature of the larva of thirty hours and later is a 

 circular shelf, which extends around the cavity of the archen- 

 teron and, when seen from the side, apparently divides it into 

 distinct compartments (PL XL, Fig. 60). Careful observa- 

 tion shows, however, that this is really a broad, very thin shelf 

 of tissue. The opening through it is at first at the center of the 

 ectoderm cavity ; later it lies at the dorsal side of the enteron. 

 Just above it is a tuft of long cilia, a modification of the general 

 ciliation of the archenteron. (See PI. XL, Fig. 60.) The first ap- 

 pearance of this structure is at about twenty-three hours, when a 

 slight constriction appears at about the middle of the archenteron. 

 Partly by the swelling out of the archenteron above and below it, 

 and partly by an active growth of the cells involved, is formed a 

 circular shelf of tissue extending out into the cavity of the ali- 

 mentary canal. In embryos of about thirty hours, if the speci- 

 men be rolled so that the proctodaeum looks upward, careful 

 focusing through the proctodaeal opening shows this circular 

 shelf running entirely around the archenteron, and extending 

 about one-half the way across its cavity. The organ at this 

 stage bears a very striking resemblance to the velum of a 

 medusa. Later it becomes very thin and vacuolated, and the 

 details of its structure are difficult to make out. The original 



