PREVIOUS INTERPRETATIONS OF CNIDARIA 



207 



coeloblastula which develops later into an invagination 

 gastrula. It has already been mentioned that no invagination 

 gastrulae can be found in Hydrozoa; their early ontogeny is 

 in reality very plastic and it can be easily changed. This can 



Fig. 37. The early ontogeny of an anthopolyp after E. Haeckel, 



be explained as being due to the partial influence of two 

 factors. One of these is the progressive trend to develop a 

 freely living larva, a planula; the second factor is the prevalent 

 role which is given to the formation of cormi. As a consequence 

 of this, the planula does not develop first into a primary 



