482 Chas. W. Hargitt 



I cannot do better than to quote in this connection from our ori- 

 ginal description ^ of P. Jonesii^ as follo ws: »To the moqtliologist a 

 form like the one just described has peculiar interest because of the 

 many primitive charaeters which are united in it. It is not impro- 

 bable that the higher calyculate Campanularian Hydroids may have 

 descended from athecate ancestors that were more or less closely 

 like the genus Perigonimus. This is a very lowly form of Tubu- 

 larians, having only a single row of tentacles, the mode of repro- 

 duction is very simple, and the medusa is of the most simple cha- 

 raeter. 



»Still while Perigonimus is treated among the naked Hydroids, 

 it has a covering. This covering is such a one as such an animai 

 as the naked Hydroids might have in their earlier stages of acquir- 

 ing a strong skeleton. It is not a highly difierentiated product, but 

 a delicate, hardly compacted slime not very unlike the mucous se- 

 cretions that all animals are so commonly throwing off from their 

 bodies. If the semi-fluid coat of this sort V7ere stiffened only a little, 

 we should arrive at the more compact, chitinous cuticle of the caly- 

 culate forms. The case of Perigonimus thus furnishes a Suggestion 

 of the probable history of the chitinous cuticle of the Hydroids: at 

 first a thin envelope, later a stiffened cover forming a greater pro- 

 tection to the body and providing for freedom of motion by the for- 

 mation of joints at stated intervals. The facts of ontogeny are in 

 favor of such a view of the history of the cuticle, for we know that 

 it arises as an excretion thrown off from the ectoderm and hardened 

 on exposure to the water. The differences between the gelatinous 

 and chitinous cuticle are such differences in the chemical or meta- 

 bolic functions of cells as might easily be conceived to come within 

 the ränge of the Operation of natural selectiou.tf 



These deductions and suggestions, while primarily the results 

 of the study of P. Jonesii^ are almost equally applicable to P. cida- 

 ritis, and more or less so to the whole genus; though certain mem- 

 bers exhibit departures from the typical generic charaeters, but not 

 of such exteut as to vitiate thera. 



Concerning the origin of the sexual cells of P. Jonesii as com- 

 pared with P. cidaritis I have not yet been able to satisfy myself 

 whoUy, not having as yet obtained medusae sufficigntly mature to 

 show any signs of germinai cells. It will not therefore be possible 



1 Op. cit. pag. 'à'à. 



