ON CTENODRILUS PARVULUS. 601 



tioa'^ clearer I will quote the following formula from Kennel. 

 Supposing we call the oldest segment 1, the second oldest 3, 

 and the youngest x, we obtain : 



Slrobilation, 1, .r, a; - 1, a; — 2 , . . 4, 3, 2. 

 Segmentation, 1, 2, 3, 4 x - %x -\,x. 



Previous to the act of division the animal generally remains 

 in a curved position, the posterior segments exhibiting inde- 

 pendent motions which were not before noticed. 



The appearance of buds is the next feature, preceding 

 division. The first bud makes its appearance dorsally imme- 

 diately behind the third segment, the second behind the fourth, 

 and so on. In Ct. parvulus we never find more than three 

 or four buds (in Ct. pardalis there may be six or more). 

 The first three segments never show any indication of budding, 

 nor do the last two or three. 



An accumulation of pigment appears in the buds as soon as 

 they show themselves. The red colour of the stomach at the 

 same time becomes materially darker. The part between two 

 segments is now very much constricted, and the bud grows 

 rapidly forward, so as to assume the shape of the head segment. 

 The previously red portion of the alimentary canal appears 

 almost black just before division, except at the constrictions, 

 where it takes the colour of the intestine. 



Zooids have the peculiarity, as long as they remain united, 

 never to develop new dissepiments. Only after the division, 

 after the breaking up, as it were, of the animal do new seg- 

 ments appear. In the true Naids, on the other hand, a diflferen- 

 tiation of the budding zones goes on to such a degree that 

 when division occurs each zooid may already be regarded as a 

 fully- developed animal. 



The first zooid in Ctenodrilus needs only to regenerate the 

 anus, and the last zooid the head. As soon as division has 

 actually taken place the zooids very soon develop into the 

 adult condition. The alimentary canal is closed at those parts 

 where it was ruptured by the constrictions, and a new mouth 

 and anus are formed in the two or three middle zooids. The 



