210 Proceedings of the Royal Physical Society. 



any species, except those recorded in this note, which have 

 been found living in streams and ponds, unless unusual floods 

 have washed them into such situations. It is therefore 

 important to notice that there are three species which are 

 largely aquatic in their habits, or four, if Criodrilus be 

 admitted. 



It may be, perhaps, a mere coincidence that in two at 

 any rate out of the four aquatic forms mentioned in the 

 present note, there is a certain approximation in structure 

 to limicoline genera, although this approximation is not in the 

 direction of any special adaptation to an aquatic life — at any 

 rate not as far as we can see at present. 



The progress of recent investigation into the structure of 

 01igoch?eta has broken down all the distinction between the 

 " Temcolte " and " Limicolae " except one, which has been, 

 on the contrary, confirmed. That distinction is seen in the 

 ova. In the Naidomorpha, Enchytrseidse, • Lumbriculidae, 

 Tubificidse, etc., the ova are few and large, the large size being- 

 due to the increased quantity of yolk stored up in the ovum ; 

 in earthworms, on the contrary, the ova are minute with 

 a very small quantity of yolk. To a certain degree Allurus 

 and Acanthodrilus Dalei ^ are intermediate in character ; the 

 ova are much larger than those of earthworms in general, 

 but are much smaller than the ova — heavily laden with yolk 

 — of such forms as Ttibifex. Without attempting — for the 

 present — to decide whether the large yolk ovum is or is not 

 the original condition in the 01igocha?ta, it is clear that as 

 both kinds of ova occur in allied forms, one must have been 

 derived from the other during the evolution of the group ; 

 and it is therefore permissible to regard the large ova of 

 Allurus and especially of Acanthodrilus as intermediate in 

 character. 



^ Named after Dr Dale of the Falkland Islands Company. 



