222 BULLETIN OF THE 



arate Nanomia from the allied Stephanomia, auct., Halistemma, Claus, and 

 Agalmopsis, Fewkes. We have on. the Florida coast an Agalmopsis, A. fragile, 

 Fewkes, which has the same knot as Nanomia, and in other particulars is very 

 near it. They are not the sanie species, although generically they seem to be 

 very close. For the present I adopt Agassiz's name, Nanomia, not because it 

 differs from other Siphonophores in the way some have thought, but on new 

 grounds, or because of the marked character of the " oil globule " in the taster 

 of Nanomia. In all other respects Nanomia is like Agalmopsis, Fewkes, from 

 the Mediterranea"n and Floridan Seas. 



It is predicted that the egg of Nanc_.na will be found to develop at first a 

 float, and then an embryonic tentacle with embryonic knobs ; that there is 

 never developed a primitive hydrophyllium ; and that an Athorybia-like cov- 

 ering scale does not form. The type of development, as compared with that of 

 Agalma, is more abbreviated, and consequently more direct in Agalmopsis 

 than in Nanomia. 



The facts which lead to this conclusion may be seen from what is said below. 

 The state of our present knowledge of the development or growth of the lar- 

 val stages of Nanomia may be shown in the following historical summary : — 



1. The larva in which the float is fully formed is traced from older larvse 

 into the genus Nanomia. This series of observations was made by A. Agassiz, 

 the discoverer of Nanomia, who considers that the youngest stage (with float 

 only) develops from a bud, and also from the egg. The earliest stage 

 which he figures he regards as identical, whether formed by either method of 

 development. 



2. Metschnikoff obtained younger stages, or those before the float is devel- 

 oped, of an allied Physophore. The youngest stage which he figures is a 

 planula. 



3. The author here describes the segmentation of the egg of Nanomia into 

 the eight-cell stage. 



The only break now in a consecutive series of obsei .ations is between two 

 and three, or the eight-cell stage and the planula. Judging from what we 

 know of other Siphonophores, no embryonic structures appear in this gap, and 

 we are justified in supposing that no primitive hydrophyllium, or covering 

 scale, appears before the float in Nanomia. 



The fact that in Nanomia no primitive hydrophyllium, such as is found in 

 Agalma, exists, does not prevent our recognizing in the youngest larva with a 

 float, and a tentacle with embryonic knobs, all the parts of the stage called 

 the primitive larva. Metschnikoff" has shown that a Siphonophore float is 

 homologous to a bell,* and I have no hesitation in accepting the theory that 

 the float of Physophores is homologous with one of the nectocalyces of the 



* The primitive larva, or, as I have elsewhere called it, the primitive medusa, 

 from which all the Siphonophores liave phylouenetically arisen, would seem to be 

 somewhat like older stajres on Plate IIL of my " Development of Agalma," Bull. 

 Mus. Comp. Zool., Vol. XI. No. U. 



