REPORT ON THE RADIOLAKIA. CXXvii 



(Pis. 120-128) have been developed from the Ccelodendrida by the formation of a 

 basal nasal tube (rhinocanna) from each galea, and the formation of a median or paired 

 frenulum, which connects the opening of the nasal tube with the apex of the galea. In 

 the Ccelodendrida, as well as in the Coelographida, there are two different subfamilies, of 

 which the more primitive (Coelodorida, Ccelotholida) have free branches from the hollow 

 radial tubes, whilst the more recent (Coelodrymida, Coeloplegmida) form an outer 

 bivalved shell Ijy anastomosis of the branches of the tubes. 



200. The Fundamental Biogenetic Laiv. — The causal connection between ontogeny 

 and phylogeny, which finds its most precise statement in the fundamental biogenetic law, 

 holds in general for the Eadiolaria as for all other organisms. In order to furnish dii'ect 

 proof of this, however, a complete empii-ical knowledge both of individual and of 

 palseontological development would be necessary. In both these directions, as has 

 been shown in the foregoing chapters, our laiowledge of the Eadiolaria is very incom- 

 plete and fragmentary, but still we are able to convince ourselves indirectly of the 

 validity of the law as applied to Eadiolaria by the aid of comparative anatomy. This 

 is now so fully known to us (§§ 1—140) that we are able not only to draw a comi^lete 

 and satisfactory picture of their morphology, but also to arrive at most important con- 

 clusions regarding the ontogeny and phylogeny of the individual groups. As regards 

 the formation of the multiform skeleton of the Eadiolaria, most of the ontogenetic 

 series of forms, with which we have become acquainted by comparative anatomy, are of 

 palingenetic nature ; that is, they are primarily due to inheritance and thus of direct 

 phylogenetic significance. On the other hand, among the ontogenetic phenomena of 

 the Eadiolaria, as far as they have yet been investigated, only very few are cenogenetic, 

 that is, brought about by adaptive modification and without direct significance as regards 

 phylogeny. 



