1882.] The Siphonophores. 91 



Prominent among all the structures which characterize the 

 Siphonophores, is the axis or stem from which the group is 

 named. In Diphyes this part (s) is very well developed, and in 

 live specimens may be seen trailing behind to a great distance in 

 the water, just as we have seen was the case in the genera of Phy- 

 sophoridae already mentioned. Along its whole extent we find 

 appendages so fastened that they do not incommode in the least 

 possible manner the direct motion of the animal through the water. 

 In the genus Diphyes it will be noticed that all the organs are 

 especially adapted for rapid motion, and as one watches these 

 graceful tubes, with their appendages, shooting through the sea, 

 the adaptation for this mode of life seems complete. With this 

 thought in mind, one can almost predict the organs of the Phy- 

 sophores which should be missed in Diphyes, and the modifica- 

 tions of their form which would be expected. 



A float would, if of any size, be a great impediment to the free 

 motion of the jelly-fish. In Diphyes, consequently, it is alto- 

 gether wanting, and other methods are resorted to in order to 

 diminish the specific gravity of the colony. 



No organ of Diphyes better illustrates the modification and 

 adaptation which has taken place to bring about rapid motion, 

 than those which move the colony, which are here, as in all 

 Siphonophores, the nectocalyces. There are only two of these 

 swimming-bells, as they arc called, and they are very different in 

 outline and general appearance from the swimming-bells of any 

 of the animals which we have yet considered. These bells differ 

 also one from the other, in size, shape and anatomy. 



At one end of the axis of Diphyes, as it floats gracefully ex- 

 tended in the water, there are two gelatinous, transparent bodies 

 of somewhat conical shape fab, pb) ; these are the two necto- 

 calyces which, with the exception of one genus, Hippopodius, are 

 double throughout all the members of the Diphyidse. 1 The con- 

 nection between the two bells at the extremity of the axis is so 

 strong, that when they are raised from the water they are not 

 broken apart, but the axis, by contraction, is simply drawn up in- 

 to a deep groove in the under side of the bell, while the appen- 

 dages, even when the colony is lifted out of water, remain attached 



more at length i„ nt genera of pipbyidar, Hippopodius has 



