84 



ACALEPIIS IN GENERAL. 



Part I. 



Flij. 49. 



as Hflix witli its iAnAX is an animal of the same order as a Limax with a rmli- 

 mentary shell, or a Tebennophorns ^vithout any shell. Similar differences occur 

 among the Ilydroids proper in the genera Coryne, Tubularia, Canipanularia, and 

 Sertulavia. In Porpita, we oljserve the same relations between the primary enlarged 

 Hydra with its tentacles and the secondary fertile Ilydra^ as in Yelella. The poly- 

 morphism in these two genera extends only to a marked difference between the 

 primary Hydra and the secondary Hydr;x), analogous to the difference there is 

 between the sterile and fertile Hydra) in Campanidaria. (Compare Firj. 15, p. 4(3.) 

 Both Velella and Porpita acqiure their full size Ijcfore Medusae buds ap])ear upon 

 their fertile Hydra?. 



In Physalia, the connnunity is also fbrnied up<ni an enlarged primary Hydra. 

 The young of this genus has been descril)ed and figured by Huxley in two 

 different stages of growth (Oceanic Hydrozoa, PI. X. Figs. 1 and 2). In the earliest 

 stage it is a simple Hydra, with a single tentacle {Fir/. 1); and while that primary 

 Hydra is enlarging and assuming its permanent character- 

 istics, other secondary Ilydra^ somewhat different from the 

 first, bud forth from it, and form with it a Ilydrariiuu [Fly. 

 2), gradually enlarging ])y the addition of others. But 

 there is this difference Ijetween such a Physalia Ilvdrarium 

 and a Velella Ilydrarium, that in the former the successive 

 secondary Ilydra? differ among themselves greatly, — some 

 acquiring a consideraljle size and having a large tentacle, 

 while othei's remain small and have a small tentacle, and 

 the proboscis of some having an open mouth, while in others 

 it remains closed. But, as I shall show hereafter, similar 

 differences are also observed among the Hydroids jiroper ; 

 so that the pecidiarities noticed in the different IIydra3 

 amount only to a more extensive polymorphism in this 

 genus than in Velella and Porpita, akin to what we have 

 already seen in Ilydractinia. As I myself have seen a 

 great many small Physalia* in the Gulf of Mexico, I may 

 add that these communities ac(|uire a considerable size 

 before any other but Hydra? buds are developed from their 

 pendent bunches. But when about one fourth the size 

 {Fig. 4!t) of the largest I have ever seen, the Medusa) 

 buds begin to make their appearance and increase in num- 

 ber, until they form distinct Medusaria combined with 

 Ilydraria ; and the whole counuuuity is then a most com- 

 plicated Hj-dro-Medusarium. The androphores and gynophores of such a community 



Physai.ia A!:i:Tni:sA, Til. 

 [ Blunt end of the air sac. supportinj; 

 the whole oomniunity, at which tlie 

 yoiingest MeUiiSie buds may be found. 

 — b Open end of the air ssic, the mouth 

 of the pvimavy Hydra. — c Crest of 

 the air sac. — m Hunches of single 

 individual.^ ; and among them the 

 youngest Medus.i; buds. — n Contracted 

 tentacle. — 1 1 Tentacles of the largest 

 kind esteudcd. 



