20 ARTHFB BENDY. 



possibly throw some light upon the origin of that remarkable 

 pelagic group of Hjdrozoa the Siphonophora, although it 

 will perhaps hardly bear close comparison with any known 

 member of that order. 



That it is an aberrant Tubularian hydroid there can, I think, 

 be no doubt, and its nearest relations appear to be the 

 enigmatical Corymorpha and its allies.^ In the genus 

 Corymorpha we also find that there is no true stalk, and 

 the curious prolongation of the body by which the animal 

 fixes itself in the sand or mud is, I believe, homologous with 

 what I have termed the float in Pelagohydra. In Cory- 

 morpha also we have a system of endodermal canals forming 

 a network around a spongy central mass, and communicating 

 at one end with the main gastral cavity. Then, again, in C o r y - 

 morpha curious processes are given off from the surface of 

 the body in the neighbourhood of the endodermal canals, 

 which may be homologous with the stolons of Pelago- 

 hydra, or possibly with the tentacles of the float. Little is 

 known, however, of the minute anatomy and histology of 

 Corymorpha, and a careful investigation in comparison 

 with. Pelagohydra is greatly to be desired. There are, 

 of course, sufficiently striking differences between the two 

 forms, but these are of a more superficial character, and 

 mainly to be accounted for by the difference in mode of life. 

 Instead of a float we find in Corymorpha a kind of rooting 

 process, and the tentacles are confined to one end of the 

 elongated body, where they are arranged in a proximal and a 

 distal set, the latter obviously representing the tentacles of 

 the proboscis in Pelagohydra. The position of the stolons, 

 between the two sets of tentacles, is totally different; and the 

 medusge also are quite distinct, for in Steenstrupia, the 

 medusa of Corymorpha, we find a single odd tentacle, 

 representing one only of the four tentacle groups of the 

 Corymorpha medusa. In both cases, however, the medusae 

 are markedly quadriradiate, and essentially similar in in- 

 ternal organisation; while in Amaltha3a, which appears to 

 * Allmau, ' Tubularian Hydroids,' p. 386, etc. 



