THE ANATOMY. SPERMATHECAE 131 



perhaps an indication of the simplification of these genera; we find only a single 

 pair of spermathecae in the Tubificidae, the Enchytraeidae (with just one exception), 

 the Naidomorpha, most of the Lumbriculidae ; Aeolosoma, the lowest of all the 

 Oligochaeta, may have as many as three pairs in segments iii, iv, v. Among the 

 higher Oligochaeta the largest number of pairs, seven, occurs in AUolobophora 

 complanata ; a few Perichaetidae have five pairs, but on the whole two pairs is the 

 prevailing number among earthworms ; the numerous exceptions prevent a comparison 

 between this fact and the existence of two pairs of testes and sperm-ducts ; however, 

 when a given species has two pairs of spermathecae and two pairs of male-ducts, 

 and when a disappearance of one pair of the one set of organs in an allied form is 

 accompanied by the disappearance of one pair in the other set of organs, there would 

 seem to be some relation between the two cases; this has happened in Acanthodrilus 

 monocystis ; the worm is closely allied to Acanthodrilus dissimilis (see below), in 

 which there is always a double set of spermathecae and male-ducts ; in the former 

 species one pair of each has vanished. Very rarely are the spermathecae median 

 and unpaired ; this state of affairs exists in the Cryptodrilids grouped together by 

 M1CHA.ELSEN into the genus Fletcher odrilus, in a few Eudrilids (e.g. Heliodrilus), and in 

 the genus Sutroa; also apparently in the Tubificid Vermiculus. The fusion in the 

 middle line of, we must suppose, originally separate and paired pouches is correlated 

 with a similar fusion of the terminal apparatus of the male-ducts. 



There seems to be no doubt, after the investigations of Vejdovsky upon Tubifex, 

 and of Beegh upon Lumbricus, that the spermathecae arise as ingrowths of the 

 epidermis ; as to the appendices of the spermathecae, where they exist, it is not so 

 certain; in Perichaeta it is common to find the appendix of large size, when the 

 pouch itself is exceedingly small ; this looks as if the appendix were phylogenetically 

 older than the pouch, and, if so, the term appendix should be dropped or appHed 

 to the pouch itself. I failed to find in immature examples of an Acanthodrilus 

 {A. falclandicus) any connexion between the appendix and the pouch; this almost 

 suggests a different origin for the two. 



In the neighbourhood of the spermathecae, or appended to them, there are in 

 a few Oligochaeta, pecuHarly modified setae, often accompanied by glands. They 

 often bear the same kind of relation to the spermathecae that the spermiducal 

 glands, with their penial setae, do to the sperm-ducts. Physiologically speaking, 

 it is possible that the correspondence is even closer. 



Among earthworms these' structures have been described in the Acanthodrihds : 

 in Acanthodrilus ungulatus, A. schmardae, and in Benhamia beddardi in their 

 complete form. In the former species the ventral setae of the eighth segment are 



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