Chap. II. MORPHOLOGY AND NOMENCLATURE. 85 



are respectively the male and female Medu,sa3 ; and l)uds of both sexes arise from 

 one and the same Hydra, the so-called gonoblastidinm. 



In Physophoridte also, the community begins with a single Hydra. Leuckart 

 (Zoologische Untersuchungen, I. PI. 2, Fig. 23), Kolliker (Schwimmpolypen von 

 Messina, PL II. Fig. 11), Vogt (Siphonophores de la mer de Nice, PI. VI. Fig. 24; 

 PI. X. Fig^. 32 and 35; and PL XI.), Gegenbauer (Beitrlige, etc., in Zeitsch. f wiss. 

 Zool. vol. 5, PL XVII. Figs. 7, 8, 9, and 11), and Huxley (Oceanic Hydrozoa, PL 

 VI. Fig. 12, and PL VIII. Fig. 2), have descrilaed and figured many such young 

 Physophorida?, exhibiting the primary Hydr;\) of different genera 

 more or less free from the secondary productions budding from 

 their sides. In the youngest of them the Hydra character is 

 ((uite plain, and their resemblance to the }'oung Physalia most 

 striking {Fig. 50). But their resemblance to the Ilydroid of 

 Nemopsis Giljliesii McCradg is still more important, since it 

 shows, beyond the possibility of a doul)t, the close affinity of 

 the naked-eyed Meduste and the Siphonophora^'. Thus far, all 

 the Medusa3 known as originating from Hydroids had Ijeen vorxu rinsoriroi:.\, 



observed to bud from Hydroids attached by their basis; but, (Copua from Gegmbau,,-.) 



f Uuiis of so-called swLnimiug-bells. 



in a recent paper (Gymnophthalmata of Charleston harbor, -6 6 so-caiied tentacles; lower i, 



so-called Polyp. — cc Feelers with 



published in tlie Proceedings of the Elliott Society of Nat. lassoceiis.-r Air sac. -slower 



6, and /•, the primary Hydra ; 



Hist, for 1858), Mr. McCrady has described a species of Ne- « and 6 secondary nydra; ; f the 



Medusa; bud5. 



mopsis, which originates from a floating, locomotive Hydroid, 



so similar to a 3"0ung Phj-sophora with incipient buds of swimming-l^ells, that, had 

 he not traced the connection of the free Medusa to its Hj'droid, or had tlie Hydroid 

 alone, with its young Medusa? buds, been observed, it would unquestionably have 

 Ijeen considered as a distinct genus lielonging to the Siphonophora^. A more direct 

 proof that the so-called swinmiing-bells (Nectocalyces) of the Physophorida? are genu- 

 ine Medusae biids remaining connected with the elongated axis of the primary 

 Hydra (the Coenosarc) from which they grow, cannot be desired. And the only 

 marked generic difference between Nemopsis and Physophora consists in the presence 

 of tentacles and sexual organs in the Medusa? of the former which become free, 

 while those of the latter are sterile and remain attached. But such diflTerences are 

 not essential among animals in which polymorphism occurs so extensively as in 

 the lower Acalephs. 



Very early the single Hydra^, from Avhicli arise the communities of Physo- 

 phorida^, bring forth two kinds of luids, — Medusa? buds on their abactinal pole, 

 and Hydrte buds on tlieir actinal pole. Thus the community at once becomes 

 a Hydro-Medusarium, consisting of one kind of Meduste which remain sterile and 

 never free themselves, and of two kinds of Hydrte ; namely, the primary Hydra, 



