PENNARIDiE. 363 



shown that at first the marginal tentacles are few, and consist of the filiform tentacles alone, the 

 clavate not making their appearance until a later period, while the oral tentacles are also entirely 

 absent in the earlier stages. When first noticed these were in tlie condition of bifid filaments, 

 and then gradually assumed the greatly ramified form which ultimately distinguished them. He 

 has also shown that as development proceeds the generative lobes gradually extend themselves 

 from the base of the manubrium downwards along the length of the radiating canals. 



Only one specimen of the trophosome has been observed. " It was floating at large, and 

 taken with the dip-net. It lived five days, developing medusae, but never fixed itself, only 

 gradually dwindling away as the medusae were developed. The tentacula were all at last retracted, 

 especially those around the broad base. In its first activity it was incessantly moving about l)y 

 means of its tentacula, mouth downwards." ^ 



Nemo2)sis Bachii is the name given by Agassiz to the medusa on which he founded the 

 genus Nemopm. As we know nothing of its trophosome, it docs not come within the range of 

 the systematic portion of the present monograph. 



PENNARIDjE. 



TROPHOSOME. — IlrDiiocAULirs developed or not. Htdkaxths with two kinds 

 of simple tentacles, one filiform, the other capitate. 



GONOSOME. — GoxopiiORES [where known] mednsiforra planoblasts, with four 

 radiating canals, and one or four more or less developed simple marginal tentacles. 



Peknauta, Goldfuss. 



JSfame. — From penna, a feather ; in allusion to the symmetrical, feather-like disposition of 

 the branches of the trophosome. 



Sertulakia, — Cavolini. 



TROPHOSOME. — HrDROPnTTON composed of a symmetrically ramified htdeo- 

 CAULUS, rooted by a creeping filiform nrDuouHiZA, the whole invested with a chitinous 



^ M'Cradv, op. cit., p. 1G3. 



47 



