110 



ACALEPIIS IN GENERAL. 



Part I. 



nature in the roscmljlance they ])Qar to the coiniiiou Medusa? of the type of 

 Aureha, Cyanea, and Pehigia (-?%■ 03), I do not believe that tlieir affinity to the 

 latter is sufficiently close to justify tlieir association with them in one and the 

 same order. (Comjjare F/'ffs. Go, GO, and G7, which are the Medusa) huds and the 

 free Medusa of the Hydroid of F/ff. G4; and F/(/s. G9 and 70, which are the Me- 

 dusfe l>uds and free Medusa of the Ilydroid of Fit/. 08, with genuine Discophorte 

 as represented in F/'t/. 03.) I take here, therefore, the group of Discophora? Crypto- 

 carpa3 {Fiffs. GG, GT, and 70) as entirely distinct from that of Discophora? Phane- 

 rocarpa) {F/'ff. 03), for which alone, I shall retain the name of Discophora\ For 

 the present, I desired only to trace the natural limits of the class of Acalephs, to 

 give examples of their various types, and to prove that the Hydroids cannot be 

 separated from the naked-eyed Medusa) any more than from the SiphonophoriE. 

 "We shall see presently that this natural division differs essentially, as an order, from 

 the Dlscophora' proper, the Hlcfjunniildludmala of Forljcs, or Acnispcda of Gegenbaur. 



Fuj. 71. 



F!<j. 73. 



Free Medusa of 



Velella mutica, Bosc. 



Proboscis. — b Radiating'chy- 



miferous tubes. — c Circular 



tube. 



Velella mi'tica, Bosc. 

 (1 So-called mouth.— n a So-calleil 

 teutacles. IJetwecu the sterile 

 tentacles and the mouth arise 

 the secondary Hydra?, or so- 

 called fertile tentacles, thegono- 

 Uastidial Polypites of Hu.\ley. 



Bum'Ii of J[odus:u of 



PlIYSALU AhETHUSA, Til. 



In various stages of develop- 

 ment. 



For tlie united Gymnophthalmata and 



Bunch of single Hydra^ and 

 clusters of Medusa; of Phy- 

 SALIA Arethi'sa, Til. 

 b b The Hydra;, with their tenta- 

 cles c f. — dd The buacbcs of 

 Medusa-. 



1 hollow base of attach- 

 ment of the whole bunch, com- 

 municating with the chymiferous 

 fy 1 • 1 ii • 1 cavity of the airsac. — ASo-called 



Hydroitlea, there is only one name accept- Poiyp. or sucker. -,/d,/rf The 



, , -, . , - p , . Medusa; buds arising from the 



able, according to tlie law of priority: simplest kind of iiydne existing 



, , 11 1 TT -r-. in the wliole community. 



tliey must be called IIydroih.e. But 

 this order must further include the Siplionophora?, since they likewise exhibit two 

 structural types, some individuals of their communities being Ilydne and others 

 Medusa', variously combined, and the Medusa) either liecoming free {Fiy. 71, derived 

 from Fig. 72) or remaining sessile {Figi<. 73 and 74), as among the majority of 

 the Hydroids proper. 



As soon as the different lainilies of this order are brought together side by 

 side, and their structure and modes of development are compared, it is impossible 

 to overlook the tyjiical conformity which exists among them, and unites them 

 all into one natural group. Had the peculiar modes of reproduction of the Aca- 

 lephs been known as early as tlieir adult condition, this affinity Avould have 

 been much sooner recognized. The idea of pedunculated Acalephs, attached to the 



