46 



ACALEPHS IN GENERAL. 



Part I. 



coinbiiuHl Thaninoenidiii (Xo]. 4, PI. XXII.) has lour distinct teiitack's and a large 

 proboscis, but neither radiating nor circular tubes. Paryidia (Vol. 4, PL XXIII.) 



f\g. 15. 



Trochopyxis, Ag. 

 New genus of Cnmpanuhiria'. 

 aa Common basis of the community. 

 — 4 Fertile Hydra, —cd Stems of 

 sterile liyiiTW. — e g Sterile Ilyilia> 

 expanded. — / Secondary sterile 

 llydra bud. 



f;-j. 16. 



Fis. 17 



also has tentacles, but of a very diflerent Ibrni, and ii large 

 proboscis, but no chyniit'erous tubes. 



In the family of Cauipanulariiv, the Hydroids seem to differ 

 greatly from the Tuliularite, the stem being horny, and the 

 bell-shaped animal surrounded by a horny IjcU ; Init a, micro- 

 scopic examination of the surface of the stem, and even of 

 the bell, of all Hydroids, shows that the only difference in the 

 outer layer of the animal consists in the thickness of that 

 h^'aline layer which in Campanularia and Sertularia ))ecoine.s 

 so firm as to assume permanent forms and to be visible to 

 the naked eye as a sort of horny sheath enclosing all the 

 soft parts, while in Tubidaria it is soft and flexible. This once 

 understood, the difference between a Campanularia [F/ff. 15) 

 and a Tubularia head is only such as we shoidd expect Ijetween members of differ- 

 ent families, — they differ in form only. Yet there is another distinction to be made 



among thein. The individuals of the same 

 commimity. imited u})ou the same stem but 

 arisuig from different axes, exhiljit marked 

 differences among themselves : the larger 

 numl)er, which have all the same form, re- 



FreeJIedl:s.v of the Cam- 

 panularia represented in uiaiu lor ever stcrilc {J^/ff- l'">, c d), while oth- 

 ers, of a different form, produce buds along 

 their internal proboscis {Fir/. Ki d^, cP, 

 d"\ d^, id', d'\ d'), which in due time free 

 themselves and swim 

 off as distinct Medusae 

 {Fii/. 17). This is, for 



E-.t, 17 —f£ r.yc,s.— (I leuiacjes. . , ,i • ,-, 



=■ '■ instance, tlie case ■\vitn 



Thaumantias and Tiaropsi.^ which are only the free Medusa; 

 of different genera of Campanularians. The same is the case, 

 again, with the Sertularians {F/'i/. 18), which produce other 



, , T\T T Dtnamena Fahricii, Ag. 



kinds Oi tree Medusa. One of the most common Ser- 



With these facts before us, there can be no doubt left '"'^'"'" "^'^™''^' °^ "" '"•''''• 



n b c .Single individu-ils ; that occu- 



in the mind of any inii>rejudiced oliserver. tliiit, even though pyinstheceii 6 is entirely, and that 



'' in cell c partly, expanded. 



the Hydroids from whicli arise many of the naked-eyed Me- 



dusa3 thus far described have not yet been ascertained, and though many Hydroids 



are known the Medusa of which have not yet been identified, enough is clearly 



Fertile Hydra of 

 Camp.inularia. 

 [ Base of attachment. — h Ca- 

 lyx. — c Digestive tube. — o 

 Mouth. — 1/1 rf2 in rf4(/S,/0 

 d'^ Medusa? buds successively 

 older. I have frequently seen 

 these buds freeing themselves 

 and assuming the form of 



Fiff. 16. It is represented 

 Iiei'e with the margin of tlie 

 disc and the tentacles raised, 

 while the proboscis is pen- 

 dent. Its adult state is de- 

 scribed in the Contributions 

 to the Nut. Hist, of tlie Aea- 

 lephs, under the name of 

 Tliaumantias. 



c Mouth and proboscis, — no 

 l:adiatiilg clivuiifercius tubes. 



Fig. 18. 



