IV VERMES— GENITAL ORGANS 261 



distinct from each other, or else the anterior and i^osterior ducts on 

 each side enter a common atrium (many LumbricuUda;), or the ducts of 

 each side unite to form a common duct, which opens outwardly without 

 the formation of an atrium {Lumbricida'). The sperm funnels lie in 

 the same segments as the testes. In those Lwnbricidce which have a 

 median sperm capsule they lie in it. 



Female Genital Apparatus. — This consists of the two ovaries, 

 the two oviducts and reeeptaeula seminis. The eggs either 

 ripen in the ovaries, or the ovaries fall into a few groups of 

 egg cells. Only one cell in each group then develops into an egg. 

 The eggs occasionally pass out of the ovaries into special egg sacs 

 corresponding to the sperm sacs, and pass out from these through 

 the oviducts. In many of the lower OUgochceta there are no 

 special oviducts. It is not really understood in what way the eggs 

 are here transmitted to the exterior. The reeeptaeula seminis are 

 paired sacs which open outwardly in special segments of the genital 

 zone. They arise as invaginations of the integument, and occur in 

 most OUgochceta in one pair, in the Lumbricidce, however, in two (less 

 often three) pairs. They are closed towards the body cavity, are in no 

 way connected with the rest of the genital apparatus, and are during 

 copulation filled with sperm from without. 



Fig. 174, which depicts the genital apparatus of Licmhricus agricola, will help to 

 elucidate the above. In the 9th and 10th segments we see the 2 reeeptaeula seminis, 

 in the 10th and 11th the sperm capsule divided by a transverse partition wall into an 

 anterior and a posterior part, with its 3 appendages (the sperm sacs) to the left ; to 

 the right the 3 sperm sacs and the cover of the sperm capsule are removed. We see 

 the anterior and posterior testes of the right side of the body, and further the 2 right- 

 hand sperm funnels and their ducts, which in the 12th segment unite to form the 

 unpaired vas deferens emerging in the 15tli segment. In the 13th segment the 2 

 ovaries lie at the 2 sides of the ventral chord. Behind these, on the anterior side of 

 the dissepiment between the 13th and 14th segments are the funnels of the oviducts 

 which open outwardly in the 14th segment. 



Polyehseta. — The description here may be brief. With isolated 

 exceptions, the sexes are separate. The matrix from which, 

 generally only at certain periods, the ovaries or testes are de- 

 veloped, is the endothelium of the body cavity. The position of 

 the germ glands varies greatly. They are sometimes found on the 

 so-called genital plates, sometimes on the dissepiments, or on the 

 mesenteries, or they may be outgrowths of the endothelial covering of 

 the ventral vessel, etc. The ovaries or testes are generally repeated 

 in many, or at any rate in several, segments. Their form varies as 

 much as their position; they are sometimes cellular thickenings, 

 sometimes massive knobs, or tufts of strands, etc. The egg or sperm 

 cells sever themselves sooner or later from the ovaries and testes, and 

 ripen when floating freely in the ccelomic fluid. From this they are 

 discharged through nephridia which are more or less strongly modified 



