246 INVERTEBBATE MORPHOLOOT. 



are as a rule hermaphrodite. It seems doubtful if the ovaries 

 have actually been made out, the large masses of ova (ov) 

 lying between the branches of the intestinal pouches, which 

 have been considered ovaries, being more probably original 

 coelomic spaces which have become filled with ova set free 

 from the ovaries ; while the so-called uterus (m), lying im- 

 mediately above the intestine, and which in mature animals 

 is closely packed with ova, is probably of the same nature. 

 Three oviducts, one dorsal and two lateral, pass from the uterus 

 to open (/o) into the rectum near its termination, though the 

 dorsal one in some forms may open directly to the exterior 

 near the anus. 



If the uterus is correctly identified as a ccelomic space, then it seems 

 not improbable that the oviducts may represent modified nephridia. 

 Their opening into the rectum is a secondary condition and does not 

 necessarily stand in opposition to their nephridial character, since practi- 

 cally the same conditions obtain in some Botifera. 



The testes {t) are branched organs lying for the most part 

 between the intestine and the nervous system, though isolated 

 masses occur in some forms near the margin of the body. On 

 each side two vasa deferentia, one anterior and one posterior, 

 convey the spermatozoa to a muscular sperm-vesicle opening 

 to the exterior at the margin nearly opposite the centre of 

 the body (ino). 



In some species, notwithstanding their hermaphroditism, " comple- 

 mental males," small individuals which possess ripe spermatozoa while 

 lacking ova, have been described as occurring. Further observations have 

 not, however, tended to confirm this idea in its original sense, since these 

 small individuals have been found to be, like the larger ones, hermaphro- 

 dites, being secondary adaptations from the prevailing hermaphroditic 

 condition, and not having, therefore, the same significance as the "com- 

 plemental males" of the Cirrhipedia (q. v). 



There can be little room for doubt but that the Myzostomeae are Annelida 

 degenerated by parasitism, and that they are most closely related to the 

 Polycheeta. It is interesting to note in this connection the effect their 

 parasitic and sessile mode of life under equable external conditions has had 

 in producing indications of a radial symmetry. 



