44 ACALEPIIS IN GENERAL. Part I. 



from these facts, that the classes of Polyps and Medusno miist he united into one ? 

 That there is a considerahle difference hetween the Medusa3 arising as huds from 

 Hydroids and the other Discophonx^ ajipears plainly from the fact, that Eschscholtz 

 has already separated them into two groups, calling the former Discophora? Crypto- 

 carpa-, and the latter DiscophoroB Phanerocarpa^ ; "while Forhes, grouping them in 

 a similar manner, calls the former Gymnophthalmata and the latter Steganophthal- 

 nuita, and Gegenhauer, Craspedota and Acraspeda. This distinction, it is true, is 

 mainly founded upon diflerences in the structure of the ovaries and spermaries, 

 of the eye-specks of the margin of the disc, and of the radiating tubes, which 

 are much fewer in the naked-eyed Medusa?, and generally simple ; but now the 

 striking peculiarity of their mode of reproduction may Ijc added to separate them 

 with more precision. 



It is important here to remark, that the so-called Hydro-Medusa? have generative 

 organs only in their Medusa state, and that the Hydroids themselves show no sign 

 of sexuality ; for I shall show hereafter that what has been considered as sexual 

 organs in some Hydroids are themselves Medusa\, differing simply from the ordi- 

 nary naked-eyed Medusae in not separating from the Hydroid stem upon which they 

 bud. The Hydroids appear, then, as a kind of larval condition of the Hydro-Me- 

 dusa> ; and, in my opinion, can no more Ije considered as genuine Polyps, than the 

 wormlike larva? of Insects can be considered as genuine Worms. For, just as by 

 a series of transformations the worm-like young of the Insect pass into the state 

 of perfect Insects, so also are the Hydroids a state of the naked-eyed Medusa? 

 preceding the maturity of the latter, and standing in a definite relation to them, 

 even though that relation be not exactly the same as that which exists between 

 the Insect larva and the perfect Insect. The Hydroids are no more a distinct 

 group of aninuxls than the larva? of Insects, and while they bear a certain resem- 

 blance to Polyps, they can no more be united with the Polyps than tlie larva? 

 of Insects with the Worms, except in as far as they belong to the same lirauch ; 

 for the Worms, as a class, stand in the same relation to the Crustacea and Insects 

 as the Polyps to the Acalephs and Echinoderms. The struct- 

 ural peculiarities that essentially distinguish the Insects from 

 the Worms appear already in their larva'', which are provided 

 with trachea? as well as the perfect Insects. And so also is 

 I the structure of the Hydroids a Medusa structure [F')/- 10), 



Campanulaku, espaniieii. and uot a Polyp structurc. The margin of the mouth spreads 



a Axis of tlie bodv. — h C;ilvx. — , n -i* ,« iiic i* j* 'j Tx*i. 



r and <? Digestive cmty. - outwarcl, autl IS uot uivcrtcd to tomi a digestive cavity distinct 



irom the mam cavity ot the body. Moreover, the main cavity 



of the body in the Hydroid has no radiating partitions, as that of the Poly})s has ; 



and this is true of all Hydroids without exception. Those from which the Medusa? 



