396 OLIGOCHAETA 



(ii) Spermathecae in vi, vii, viii, ix (fifteen species). 



p. martensi, Mich. 



P. divergens, Mich. 



P. nipponica, F. E. B. 



P. dyeri, F. E. B. 



P. sinensis, F. E. B. 



P. darnleiensis, Fletcher. 



P. peregrina, Fletchee. 



P. vordermanni, Hoest. 



P. enganensis, Rosa. 



P- neoguinensis, Mich. 



P. modigliani, Rosa. 



P. vaillanti, F. E. B. 



P. feae, Ros.a.. 



P. indica, Hokst. 



P. posthuma, Vaillant. 



E. Five pairs of spermathecae. 



(12) Spermathecae in v, vi, vii, viii, ix (two species). 



P. pentacystis, RosA. 

 P. violacea, F. E. B. 



It is clear from the above lists that two is the prevailing number of spermathecae 

 in the genus Perichaeta. In all twenty-six species have but two pairs of spermathecae. 

 The next commonest number is four ; but there are only seventeen species which have 

 four spermathecae as against sixteen which have three pairs. Eight species have only 

 a single pair, and the rarest condition is to have five pairs ; only two are in this 

 condition. It will also be observed that where there are fewer than five pairs of 

 spermathecae they occur in one or more of the segments occupied by those five. It 

 seems, therefore, as if the fewer spermathecae could be derived from the larger number 

 by a reduction ; as, however, there is no species known in which the single pair of 

 spermathecae are in segment v, it also appears as if the original number of sperma- 

 thecae were rather four than five. And this suggestion coincides with the fact that 

 the largest number of species whose spermathecae are constant to a given series of 

 segments are those in which the spermathecae are in segments vi-ix. It is not however, 

 possible, at least so far as we know at present, to classify the species of Perichaeta 



