RELATIONS OF SAGITTA BIPUNCTATA. 21 



which, according to Mr. Huxley, are disposed in three distinct 

 sets. As has been before stated, the eyes are lodged in the 

 upper surface of the optic ganglia, and contained together 

 with them in special cavities excavated in the integuments of 

 the head. 



2. Trunk. — This portion, which constitutes the principal 

 part of the animal, is an elongated hollow sac containing the 

 muscular hands above described, the intestinal canal and ter- 

 mination of the oesophagus, together with the ventral ganglion 

 and its branches, and the ovaries which are situated poste- 

 riorly. 



The intestinal canal, which commences at the termination of 

 the oesophagus, is a simple, straight, somewhat compressed 

 tube, extending from this point to the junction of the trunk 

 with the caudal portion, where it makes a rather abrupt 

 curve downwards, becomes contracted, and terminates in the 

 anus, which presents the form sometimes of a rounded aper- 

 ture, sometimes more that of an elongated slit, but in either 

 case projecting beyond the surface. The walls of this simple 

 tube are composed principally of a layer of annular fibres, 

 strengthened on the upper and under sides by a narrow band 

 of longitudinal fibres, which, according to Krohn, are situated 

 external to the annular. The tube is lined internally by an 

 epithelium, composed of elongated prismatic cells, furnished, 

 perhaps throughout, with long vibratile cilia. It is supported 

 in its place above by a continuous median band, and below it 

 is held by numerous slender, usually branched threads, disposed 

 in a line corresponding to the band above. The perigastric 

 cavity is thus imperfectly divided, as it were, into two lateral 

 compartments. 



The intestinal canal is generally empty, but in a few instances 

 Krohn has seen in it fragments of minute fish and Crustacea, 

 and in some cases portions of other Sagitta. 



The " caudal portion," and the ovaries, constitute the sexual 

 apjmratus, which will now be described. 



1. The female portion of this apparatus consists of two 

 organs, which are situated in the posterior part of the cavity 

 of the trunk, on either side of the terminal portion of the in- 

 testine (fig. 4, a, a, fig. 6). These organs, which may be 

 termed ovaries, in the mature state, are often of considerable 

 size, extending even beyond the upper pair of lateral fins. 

 They are elongated sacs, which are attached by a longitudinal 

 band to the lower wall of the trunk. Inferiorly the ovary 

 curves abruptly upwards and outwards, forming a sort of short 

 oviduct, which opens externally between the upper muscular 

 band and the base of the posterior pair of lateral fins. In the 



