ORDER OASTROTRICHA. 197 



while at the other they open 011 the ventral side of the body 

 to the exterior. The reproductive system (pv) consists of two 

 groups of germ-cells lying in the posterior part of the body, 

 one on each side of the digestive tract, but no oviduct has been 

 definitely made out to exist. With regard to the testes some 

 uncertainty exists, an oval body lying in the same region of 

 the body as the ovaries, but beneath the intestine, having been 

 described as such an organ, though the identification is open 

 to question. If, however, the body in question be the testes, 

 the animals are hermaphrodite. As in the case of the female 

 organ no ducts have been observed leading from the testes, 

 and nothing is known as to the method by which the sexual 

 products are extruded. 



The nervous system (ri) consists of a large ganglionic mass 

 which lies above the oasophagus in the head region, and from 

 the posterior border of which two processes, one on each side 

 of the middle line, are directed posteriorly and dorsally, 

 perhaps representing the origin of a pair of nerves, while the 

 postero-exterual angles of the gangliouic mass are continued 

 backwards to near the posterior extremity of the body to 

 form the lateral nerves. Certain of the elongated cilia found 

 on the head no doubt function as sense-organs, coming into 

 intimate connection at their bases with the cells of the supra- 

 03sophageal ganglion ; in addition to these sense-organs eyes 

 have also been described as occurring in some species, either 

 in the form of simple patches of pigment lying in the integu- 

 ment above the brain, or else of such patches provided with 

 lens-like structures. 



The affinities of the Gastrotricha seem almost certainly to be with the 

 Kotifera, many of the structural features being exceedingly similar in the 

 two groups. The principal differences are to be found in the arrangement 

 of the cilia and in the structure of the nephridia. With regard to the 

 former it seems not improbable that in the arrangement seen in the Gastro- 

 tricha a relic of a more primitive uniform ciliation is presented, and that 

 in this particular as well as in the greater simplicity of the digestive tract, 

 and in the general form of the body and life-habits, the Gastrotricha 

 approach more nearly an ancestral Turbellarian form than do the Rotifera. 

 The nephridia depart much more widely, however, from the Turbellarian 

 condition than do those of the Rotifera a fact which argues against the 

 more primitive character of the ffastrotricha, as does likewise the absence 

 of ducts for the reproductive organs. Whether, therefore, the Gastrotricha 



