338 



ALFRED GIBBS BOURNE. 



segments immediately following the peristomial segment ; and, 

 moreover, the number of segments thus modified (cephalized) 

 appears to be constant in all the species of a genus.^ The 

 accompanying woodcut shows the various generic types. 



The laws which govern gemmation or budding were worked 

 out by Semper. I have added the following remarks upon the 

 subject with the view of making this somewhat complicated 

 matter clearer to English readers, in the hope that some 

 microscopist may be induced to make further observations on 

 the subject in species where we still lack information as 

 to the budding individuals. There are many such, but there 

 are an even greater number of species in which the sexual 

 individuals have never been seen. 



In the following diagram — 



' The only recorded exception to this which I have found is given by 

 Bousfield (1. c.)j who states that in D. f urcata there are only four segments 

 destitute of dorsal setse, while in all other species there are Ave such seg- 

 ments. I may, however, point out that D. f urcata differs in another 

 marked character from all other known species of Dero in the possession of 

 " palpi," and should, I expect, be therefore placed in another genus. 



