362 



OLIGOCHAETA 



the end of the spermiducal gland ; in the Perichaetidae the gland 

 is differentiated into two sections; there is a muscular duct 

 leading to the exterior, and a lobate glandular part, which is 

 formed by a complicated branching of a single sac such as 

 exists in the Tubificidae ; in the Acanthodrilidae and in many 

 Cryptodrilidae the spermiducal glands are of a tubular form 



and are not branched, though 

 there is the same differentia- 

 tion into a duct and a secreting 

 portion. There are in the Acan- 

 thodrilidae two pairs of these, 

 and as many as three pairs in 

 Dichogaster ; in the latter case 

 in three successive segments. 

 In the Acanthodrilidae the 

 glands are upon the seventeenth 

 and nineteenth segments. In 

 most Cryptodrilidae the sperm- 

 ducts do not open into the duct 

 of the spermiducal gland, but 

 on to the body-wall near to its 

 orifice, the distance varying in 

 different genera. In the Acan- 

 thodrilidae the male pore is on 

 the eighteenth segment, re- 

 Fio. 192. Diagrammatic longitudinal sec- moved therefore by the distance 

 tion of Lumbric, showing the generative o f a segment from the aperture 



segments. x 3. (After Hesse.) sp, r 



Spermathecal pore ; t, testis ; s.s, seminal OI Cither OI the glands. It 



_ _ 



structures which exist in Micro- 

 chaeta benhami * and in other Geoscolecids, and which have been 

 termed copulatory glands, are the equivalents of the spermiducal 

 glands. 



In many earthworms there are, at the external opening of the 

 male ducts, bundles of specially modified chaetae, which have been 

 called, from their supposed function, penial chaetae ; they are 

 usually ornamented at the free end with spinelets or ridges, and 

 frequently offer valuable specific characters. In the Lumbricidae 

 and the Geoscolicidae there are modified chaetae upon the 

 1 See Dr. Rosa in Ann. Hofmus. Wicn, vi. 1891, p. 379. 



