Chap. II. 



LIMITS OF THE CLASS. 



Ill 



ground, must have appeared unnatural to those who were fliniiUar with the large 

 free Medusa? so common everjAvhere ; and it is hardly a matter of surprise that 

 even now, there should be naturalists who oppose the views I have here pre- 

 sented. Let it be remembered, however, that it is not so very long since the 

 pedunculated Crinoids were arranged among the Polyps, and that it has only 

 required a direct comparison between them and the free Crinoids to show their 

 close affinity with the other members of the class of Echinoderms. Now, the 

 pedunculated Hydroids bear the same relation to the swimming Hydroids (the 

 Siphonophorai) as the peduncidated Crinoids bear to the free Crinoids ; and, the 

 close affinity of the Siphonophorfe and Hydroids proper once admitted, their mode 

 of reproduction renders their separation from the higher Acalephs forever impossible, 

 while it forbids, at the same time, their association with the Polyps. 



That Lucernaria {Figs. 75 and 76) and 

 Millepora [Fiys. 77, 78, and 79) belong to 

 the Hydroids proper has already been shown 

 (pp. 59 and 61). The nearest affinity of 

 Millepora is with Hydractinia (compare Figs. 

 61 and 62) ; but its mode of reproduction 

 has thus far remained unknown. 



Fig. 75. 



Lucernaria, 



Seen in profile. 

 [ Peduncle. — b b Tentacular 

 bunches. 



FUj. 



Fifj. 78. 



Lucernaria, 



Seen from above. 

 m Moutli. — c c Ovaries. 

 h h Tentacular bunches. 



Fig. 79. 



Millepora alcicorni.s, Lmk. 



A branch of the Coral of that 

 name, natural size. The little pro- 

 jections along the edge are meant 

 for the extended Polyps. They are 

 extremely shy and delicate, and 

 never show themselves again after 

 a branch has once been taken out 

 of the n-ater. 



Millepora alcicornis, Lmk. 



Magnified view of the extended 

 Polyps or Hydroids of the same 

 Coral stock. 

 a rt Smaller Hydroids. — h Larger Ily- 



droid, 7/1 its mouth, ( its tentacles. 



Millepora alcicoenis, Lmk. 

 Transverse section of a branch of 



the Coral stock, magnified. 



o a Pits of the Hydroids, with their suc- 

 cessive floors. It is very difficult to 

 obtain sections of the pits occupied 

 by the smaller Ilydroids. 



The structural features of all these various representatives of the class of Aca- 

 lephs will, of course, be more fully illustrated in the following chapters. My 

 object here was mainly to show, upon the most general evidence, what are the 

 types of Radiates that constitute the class of Acalephs, and incidentally to call 

 attention to their special affinities. If the views I entertain upon this sulyect are 

 correct, this class embraces three orders, — the Ctenophor.e, the Discophor.b proper, 

 to the exclusion of the naked-eyed Medusa^, and the Hydroid.e, including the 



