106 PROFESSOR ALLMAN ON THE GENETIC SUCCESSION. 



clusters, surrounding the hydranth in a sort of verticil (fig. 9). Each cluster 

 consists of sessile gonophores, borne on a greatly depressed common peduncle, 

 and thus recalling the form of inflorescence known as a capitulum. The order 

 of development, however, appears to be centrifugal, instead of being, as in the 

 true capitulum, centripetal, and would therefore, perhaps, more truly suggest 

 a comparison with the depressed cyme which constitutes the axillary inflores- 

 ence in many Ldbiatce. 



In the comparison just instituted between the gonsome of the Hydrohla 

 and the inflorescence of plants, it will be noticed, that whenever' in the 

 Hydroida the generative buds are borne upon a special gonsomal axis, like 

 the flowers in an inflorescence, the order of succession is far more frequently a 

 centrifugal than a centripetal one. In the calyptoblastic forms, indeed, it is 

 always centrifugal. This is exactly the opposite of what prevails in plants ; 

 for here the centripetal forms of inflorescence greatly exceed the centrifugal 



ones. 



We must be careful, however, not to assign to the resemblances which may 

 be noticed more importance than they are justly entitled to. But yet, after 

 setting aside such as are merely superficial and accidental, many still remain 

 which have their origin in certain deep-seated properties, and may be referred 

 to the common phenomenon of gemmation, which by agamic multiplication in 

 the animal as weU as in the plant, gives rise to colonies whose members in each 

 case, mutually dependent on one another, continue to be organically associated 

 into definitely arranged and determinate groups. 



