\ui REPRODUCTIVE ORGANS 361 



Enchytraeidae. Elsewhere the oviducts are a pair of tubes with 

 a wide, funnel-shaped, and ciliated mouth, which leads to the 

 exterior by way of a ciliated tube of varying length. 



The sperm-ducts are of an essentially similar structure ; but 

 they are commonly much longer, passing through a variable 

 number of segments on their way to the exterior. In most earth- 

 worms there are, moreover, two of them on each side instead of 

 only a single pair, as is the case with the oviducts. Among the 

 Tubificidue, Naids, and other aquatic families there are only two 

 sperm-ducts, one on each side of the body. But this is not a 

 character of the aquatic families, for the Lumbriculidae have 

 generally two pairs, as in the earthworms. It is, however, a 

 rule with hardly an exception, that among the aquatic Oligo- 

 chaets the sperm-ducts open, as do the oviducts in all Oligo- 

 chaets, upon the segments following that which bears internally 

 the ciliated funnel It is only in the Moniligastridae among 

 earthworms that the sperm-duct only traverses two segments in 

 its course. But where it is short as regards the actual distance 

 traversed between the two extremities, the tube itself is com- 

 monly long and coiled. 



Sometimes, as in our common earthworms, the sperm-duct 

 opens directly on to the exterior of the body, the lips of the 

 external orifice being swollen by the development of cutaneous 

 gland-cells. In the majority of cases the sperm-duct or ducts 

 open near or into a glandular structure which in earthworms has 

 been called " prostate " ; in the aquatic forms, on the other hand, 

 " atrium." As these terms are objectionable from the different 

 way in which they have been used for structures of Vertebrates, 

 I have suggested for both the term " spermiducal glands," indicat- 

 ing the identity of the structure in all Oligochaeta. The number 

 of pairs of these glands varies, as does also their shape and size. 

 The typical form is perhaps illustrated in the lower Oligochaeta, 

 where there is but a single pair into which the sperm-duct or ducts 

 of the same side open. The Naids, Tubificidae, Lumbriculidae, and 

 Moniligastridae have a simple gland of this description on each side 

 of the body. These glands may consist of a tuft of pear-shaped 

 glandular cells attached to the organ at one side, as in most 

 Tubificidae, or of a complete investment of gland -cells, as in 

 Bmnchiura. Among earthworms it is only the Moniligastridae 

 and the Eudrilidae in which the sperm-duct opens directly into 



