1 82 Introductio7i to Animal Morphology. 



The sexes are separate, except in Pelodytes, 

 Filaria, and Ascaris nigrovenosa. The organs are 

 large, and produce large quantities of sexual pro- 

 ducts. The male possesses one, rarely two, ventral, 

 convoluted, tubular testes, ending in a vas deferens 

 leading to a seminal vesicle, often villous within. 

 The duct opens beside the anus, and is armed with 

 one or two chitinous spicules, arising from muscular 

 pouches. The epithelium of the testis is ovoidal, of 

 the vesicle and duct flatter. The female possesses 1-5 

 convoluted tubular ovaries ; usually two, uniting at the 

 pre-anal, often medio-ventral, vagina, which equals 

 the spicula in length. Sometimes there are two 

 papillae midway between the anus and tip of the tail, 

 in Pelodera appendiculata prolonged into ribbon-like 

 appendages. The first part of each ovary may be 

 germigenous, the next partvitelligenous, and this may 

 join the terminal dilated part or uterus by a narrow 

 tube (Leptodera appendiculata). The sexual tubes 

 are first filled with granular protoplasm, which forms 

 a central rachis, on which the eggs or the mother- 

 cells of the spermatozoa develop. In some of the few- 

 hermaphrodite forms, both products develop in the 

 same tube, sperm-cells first, afterwards ova, as in the 

 parasite form of Ascaris nigrovenosa (which has a 

 female appearance). Some species are viviparous, 

 others lay hard or soft-shelled eggs, a few have a 

 metamorphic development ; thus Urolabes palustris 

 is the larva of Filaria Medinensis. The eggs of 

 Dochmius trigonocephalus of the dog develop into 

 Rhabditis-like forms in water, and after several 

 moults, again enter the dog's intestine with its drink, 

 and in twenty-four days lose the stomach teeth, and 



