COMMON EARTHWORM. 



207 



The testes of Microchaeta are four in number as in Lumbricus, and are con- 

 tained in the vesiculae. The organs in Earthworms usually described as testes 

 appear to be the vesiculae. Of these there are generally two pairs ; in certain forms, 

 however, only a single pair, which extends through three somites in Urochaeta and 

 Typhaeus, through twelve to fifteen in Titanus, and thirty or more in Urobenus 

 (Benham). There is always a single pair of ovaries, which in Plutellus are situated 

 in front of the testes. The ovaries may be lobed, e. g. in some species of Peri- 

 chaeta. There are four separate vasa deferentia in Moniligaster and Acanthodrilus, 

 each with its own aperture : and they each appear to possess, as does the 

 vas deferens of the aquatic Oligochaeta, a terminal vesicle homologous with a 

 nephridial vesicle. The ciliated funnels are in front of the vesiculae in Pontodrilus 

 Marionis, while Anteus is stated to possess no sperm-ducts at all. The genital 

 apertures are sometimes approximated ventrally and the oviducal aperture is 

 single, and median in Perichaeta, Perionyx, and sometimes in Megascolex. The 

 position of the male apertures with reference to the clitellum varies, and has been 

 used by Perrier as a means of classifying Earthworms. The apertures in question 

 are situated (i) in front of the clitellum, Ante-clitelliani, e.g. Lumbricus \ (2) 

 within it, Intra-clitelliani, e. g. Anteus, Titanus, Urochaeta : (3) behind it, Post- 

 clitelliani, e. g. Perichaeta, Megascolex, Plutellus, Pontodrilus, Acanthodrilus, Peri- 

 onyx : (4) or there is no clitellum even in sexually mature specimens, Aclitelliani, 

 e. g. Moniligaster. Megascolex has been termed by Beddard Infra-clitellian, for 

 though the vasa deferentia open within the clitellum, yet they occupy a non- 

 glandular ventral area. As to the other accessory organs of generation, the setae 

 of the male somites are sometimes much enlarged, especially in the genera 

 Acanthodrilus and Eudrilus-, copulatory papillae are present in some species of 

 Perichaeta ; and prostatic glands opening into the sperm-ducts are found in the 

 worms just named. The spermathecae are always in front of the vesiculae ex- 

 cept in Microchaeta and Eudrilus. They vary in number and size even in the 

 same genus, and are sometimes complicated as in Perichaeta Houlleti by the 

 addition of glands. There may be more than two spermathecae in each somite : in 

 this case they are arranged in transverse rows. See Beddard, A. N. H. (5), xvii. 

 1886, pp. 91-92 and 93-94: Benham, Q. J. M. xxvi. pp. 263, 280. 



In the aquatic Oligochaeta the nephridia atrophy away in the somites in which 

 the sexual glands and ducts are undergoing evolution. In Lumbricus and many 

 other Earthworms the two sets of structures co-exist. Vejdovsky is inclined to 

 suppose that the larger size of the coelome is the cause of this persistence. The 

 evolution of the genital ducts in the Earthworms remains to be worked out \ In 

 many aquatic Oligochaeta it is accurately known. The vas deferens has in them a 

 funnel, and a ciliated tube derived from peritoneal epithelium, and an atrium 

 which is invaginated from the hypodermis like the nephridial vesicle, but is not 

 represented in most Earthworms. The spermathecae are invaginations of the 

 same kind. The oviducts are either simple slits (Aeolosoma, Chaetogastridae, &c.) 

 or a pair of funnels (Lumbriculidae), and are obviously degenerate. Vejdovsky is 

 inclined to conclude (op. cit. p. 161) that the sexual ducts either correspond to all 

 the parts of an ordinary nephridium (vasa deferentia of aquatic Oligochaeta, of 

 Acanthodrilus and Moniligaster) or to some of them (spermatheca to the nephridial 

 1 Bergh states that he intends to publish on the subject. 



