ON THE BRITISH SPECIES OP ORFSIA. 181 



In another case the formula (15 + r^ + (9) + (10) + {9+r^) 

 was obtained, and it is obvious that this is a further illustration 

 of the same principle. 



In an axis, part of the formula of which was (13 + r^ + 

 (14 + a?" + rj) + (11 + /), one of the internodes had two 

 branches, the first developed on the side of the basal zocecium, 

 and the second on the opposite side. Since the number of 

 zooecia in this internode was even, the regular alternation of 

 the branches was not disturbed. Cases of this kind appear to 

 be extremely rare. 



Another abnormal case, from a young colony, had the 

 formula — 



+ (5+r») + 



'=(7) + (6 +^2) + (8) + (6) + (2 +:j;) 



Here it is obvious that the whole of the lateral branch shown 

 is very abnormal ; the first branch is developed by the second 

 internode, which has an even number of zooecia j and it is on 

 the same side as the basal zooecium of the first internode, and 

 on the opposite side to that of its own internode. Here it must 

 be supposed that the tendency to produce the first branch on 

 the abaxial side has prevailed over the tendency to produce a 

 branch on the side of the basal zooecium of an internode. 



In one case observed, in which the base of an old colony was 

 regenerating fresh branches, two small growing-points were 

 seen to have been formed, almost exactly opposite one another, 

 from the same internode. If this growth had proceeded some- 

 what further, it might not have been obvious that the abnormal 

 character of the branching was due to the occurrence of regene- 

 rative processes, in which the regularity which characterises the 

 normal branching does not seem to be so marked. 



Some of these remarkable relations are obvious enough in 

 the figures given by previous authors^ none of whom seem, 

 however, to have been struck with the general rule illustrated 

 by these cases. Thus Milne-Edwards/ in pi. vii, fig. 1 b 

 (C. denticulata), shows a portion of a colony in which two 

 1 ' Ann. Sci. Nat./ 2^ s6r., " Zool.," tome ix. 



