130 OLIGOCHAETA 



The following table shows all the different segments which may be occupied by 

 the spermathecae in the Oligochaeta : 



Segment iii . . . . Aeolosoma. 



Segment iv . . . . Aeolosoma. 



Segment v Perichaeta. 



Segment vi . . . . Perichaeta. 



Segment vii . . . . Perichaeta. 



Segment viii .... Perichaeta. 



Segment ix . . . . Perichaeta. 



Segment x . . . . Allolobophora. 



Segment xi Allolobophora. 



Segment xii .... Allolobophora. 



Segment xiii .... Microchaeta. 



Segment xiv . . . . Microchaeta. 



Segment xv . . . Kynotus. 



Segment xvi . . . . Microchaeta. 



As a rule there is a certain relation between the position of these organs and that 

 of the testes. Thus in Aeolosoina, where the testes are in the fifth segment, the 

 spermathecae commence in. the third; in the Naidomorpha they lie in the same 

 segment as the testes, viz. the tifth ; this is also the ease with the Tubificidnc ; 

 both testes and spermathecae are in the tenth. In earthworms the spermathecae 

 generally lie in front of the testes ; but in the Lumbricidae they are often in the 

 same segments. No very definite relation between the position of the spermathecae 

 and that of any other organ can be traced ; any attempt to trace such a relation is 

 rendered difficult by numerous exceptions. It is only in certain Lumbriculidae and 

 in Phreodrilus that the spermathecae are behind all the reproductive organs. They 

 appear never to be placed behind the clitellum. 



As a rule each segment of those which contain them has only one pair of sperma- 

 thecae ; among the Geoscolicidae, however, a very large number of spermathecae 

 sometimes occur in a single segment ; thus in Kynotus madagascariensis there are as 

 many as fourteen pairs in one segment. Perichaeta sangirensis, and a few allied species, 

 Allolobophora savignyi, are the only worms not belonging to the family Geoscolicidae in 

 which numerous spermathecae take the place of the more usual pair. This great increase 

 in numbers is accompanied by a reduction in size, more marked in the Geoscolicidae 

 than in the Perichaeta. When the spermathecae are paired, the number of pairs 

 varies from one to seven. One is the usual number in the lower forms, and is 



