THE GONOPHORES OF THE HYDEOCOEALLINiE. 389 



The peculiar characteristics of the group, namely, the 

 dimorphism of the polyps and the extensive skeleton of car- 

 bonate of lime, have not been considered by naturalists to be of 

 sufficient importance by themselves to justify the separation of 

 the Hydrocorallinse from the Hydromedusse. 



Lankester (9) places them in a separate order of the sub- 

 class Hydromedusae. 



In the classification used at Cambridge Balfour placed Mille- 

 pora and the Stylasteridse in the sub-order Hydroidea of the 

 order Hydromedusae. 



Claus, in his ' Grundzuge der Zoologie,^ makes the Hydro- 

 corallinae the first sub-order of the order Hydromedusae. 



In Jackson's edition of Rolleston's ' Forms of Animal Life ' 

 (8) the order Hydroidea is divided into the three sub-orders 

 (1) Tubulariae, (2) Hydrocorallinae, and (3) Campanularise. 



The opinion I have come to, based upon Moseley's researches 

 and my owu, is that the Hydrocorallinae should be placed in 

 an order apart from the Tubulariae and Campanularise (i. e. 

 Hydroidea of Balfour and Jackson). 



The classification of the Hydrocorallinae with the Hydroidea 

 was perfectly justified by the state of knowledge at the time. 

 Both dimorphism and skeletal structures are, comparatively 

 speaking, uncertain features for the purposes of classification, 

 and the character and structure of the polyps and their con- 

 necting canal systems show undoubted afl&nities with many 

 forms of Tubulariae. 



Unless, then, the organs that bear the sexual products can 

 be shown to differ very widely from those of the Hydroidea, 

 and present characteristics peculiarly their own, the Hydro- 

 corallinae must remain in the position that is assigned to them 

 by some authorities in the order Hydroidea. 



These considerations demand a careful and exhaustive com- 

 parison of the typical gonophores of the Tubulariae, and of those 

 Hydrocorallines that are at present known to us. 



To aid in the discussion of the homologies I have given on 

 p. 390 diagrammatic figures representing the structure of 

 (Woodcut 2) a phanerocodonic medusa, (3) a medusa of Mille- 



