ANATOMY OF POLY.NOE. 65 



gives off in each somite to the rear of the muscular pharynx, a right 

 and a left glandular pouch or caecum, whose function we are yet uncer- 

 tain of. Curiously enough, the anus is not terminal, but, as in the 

 Copepoda, is found upon the dorsal surface of the penultimate 

 segment. 



A definite respiratory, or pseud-haemal system, was long denied 

 to the Aphroditida?, bat Salenka and others have demonstrated in 

 Aphrodite and other species, a highly developed series of fine closed 

 tubes containing fluid apparently respiratory in use, but almost 

 invisible because of its all but entire lack of colour. 



These vessels are in no way concerned with the diffusion of 

 digested nutriment. That duty is taken charge of by a corpusculated 

 fluid filling the general cavity of the body (Coelome), and which 

 circulates readily through the whole length of the body by reason 

 of gaps being present in the septa that break the coelome up into 

 numerous chambers. 



Each of the septa here mentioned is a vertical partition wall 

 or rather transverse membranous mesentery, parting the coelome of 

 adjacent somites throughout the greater part of the body, but 

 suffering modification in the anterior portion of the animal, where 

 the evertible pharynx requires special freedom of movement. 



The nerves consist of a large cerebral mass above the mouth, 

 connected by a commisure passing on either side of the pharynx, 

 with a chain of ganglia in the ventral wall of the body. In reality 

 this chain is double, but is so far coalesced as to appear single. 

 Each somite possesses one of these double ganglia. From the upper 

 and anterior edge of the cerebral nerve mass, nerves are given off to 

 the median and to the superior lateral antenna?, while the palps are 

 innervated from the ventral surface. Segmental organs, excretory in 

 function, are also present, but extremely minute. 



REPRODUCTION. The sexes are separate, but no special ovaries' 

 or testes are present ; the genital products being developed as cellular 

 masses from the internal surface of the body walls. The products 

 ripen and are set free in the coelome, whence they obtain egress, 

 either by rupture of the body- wall, or by way, perhaps, of the 

 sogmental organs in some cases. 



The embryos have the characteristic Polychsete form, being 

 trochophcres, that is, they are rounded bodies with an encircling 

 band of cilia immediately in front of the mouth, the portion in 

 front of the band, forming the prse-oral region already referred to 

 as the precursor of the adult prostommm. 



Adult form is soon assumed, but for some time after EO doing 

 the young pursue a pelagic existence, swimming freely on the surface 

 of the sea, and frequently falling victims to the snare of the tow-net. 



