CNIDARIA 75 



of the Siplionophoi'e organism were established. We might 

 perhaps be led by such considerations to I'ecognize in those 

 forms with a persistent apical stigma (Rliizophysas, Physa- 

 lias) the most primitive of the now existing Siphonophores. 



In this proposed hypothesis of the derivation of the pneumatophore we 

 are opposed to the conception, shared in by most investigators (comp. 

 p. 72), that it is a modified medusa-beU. The latter view is founded 

 partly on the structure of the fully developed pneumatophore and i^artly 

 on its development. Even though the spaces of the gastrovascular 

 system in the vicinity of the pneumatophore, divided as they are by 

 septa, challenge a comparison with the I'adial canals of a medusa, and 

 even though the bud-like fundament of the pneumatophore is uncommonly 

 hke a medusa bud, as has been stated by Metschnikoff (pp. 62, 63), these 

 resemblances do not appear to us to present proofs of a compulsory 

 nature, the more so since the transition from a medusa into a hydrostatic 

 organ involves a change of function that is somewhat difficult to compre- 

 hend. According to our way of looking at it, on the contrary, the apical 

 position of the pneumatophore, sunk into the upiDermost end of the stem, 

 and its early appearance in the ontogeny of many forms, are most easily 

 explained. 



According to our notion, the pneumatophore would be the most primi- 

 tive locomotor organ of the Siphonophora, to which a nectosome would 

 be added only secondarily. Accordingly the Physophorida3 would repre- 

 sent the more primitive forms, and the Calycophoridfe derived forms, 

 with divergent development caused by the loss of the pneumatophore 

 and the in part higher differentiation of the nectocalyces. Among the 

 Physonectte (Haeckel) the Apolemidte, the nectosome of which is still 

 provided with heteromorijhous individuals, would perhaps represent the 

 most primitive branch. Opposed to this theory, however, is the fact that 

 histologically the Calycophorida? exhibit the simplest conditions (Kokot- 

 neff) ; but these might have been simjjliiied secondarily. 



When with the above statements we adopt the hydroid 

 theory founded by Lkuckart, it is hereby to be understood 

 that, according to our point of view, the existing facts ai-e 

 most easily explained by this theory. Nevertheless we can 

 as yet ascribe even to it only a certain degree of proba- 

 bility. 



II. ANTHOZOA. 



Alcyonaria. — The sexual products of the Anthozoa, which 

 arise from the entoderm (Hertwig, No. 9), undergo the 

 process of ripening in sexual organs which belong to the 



