ACALEPH^. 177 



which are applied to the prey seized and benumbed by the tentacles 

 If the prey be small, it is sucked bodily into the gastric sac ; if large 

 the sac becomes distended with its juices and dissolved parts, the 

 gastric secretion being a very rapid and powerful solvent. The 

 mouth of each sac is wide, with a broad everted lip, armed with a 

 series of " nettle-cells." The whole gastric appendage is highly 

 contractile and in constant motion in the living animal. The ap- 

 pendages of the third class are cyathiform ; the development of gene- 

 rative parts has not yet been followed out in these. The question of 

 the genetic cycle of the Physalia is one of the most interesting that 

 remains open to the observations of the naturalist who may traverse 

 the tropical seas where they most abound. 



The Physophora differs from the Physalia in having, besides the 

 principal or axial air-bladder, a number of smaller ones appended to 

 it, placed one below the other, and forming by their aggregation 

 prisms or cylinders : the tentacles, as in Physalia, are of three kinds : 

 some are filiform, beset with thread-cells and cirri, susceptible of 

 much elongation ; the others form a racemose cluster at their lower 

 extremity, e. g. in the Physophora hydrostatica : some form groups 

 of pyriform or spherical vesicles ; a third kind are short and conical, 

 and perform the office of digestion. The sac or body is defended by 

 substances of cartilaginous hardness. Only the external membrane 

 of the air-bladder appears to be perforated in the Physophora. For 

 the description of a compound form of physograde Acalephe, forming 

 the genus Siephanomia, I may refer to the excellent paper CXLVI. 

 p. 217. 



The genus Diphyes presents a long, conical, subangular body of a 

 cartilaginous firmness, closed and pointed anteriorly, with two wide 

 apertures at its base : the upper of these is the outlet of the cavity 

 containing the air-vesicle, and is called the natatorial cavity ; the lower 

 orifice is that of the nuclear cavity, from which issues a tubular ten- 

 tacle, with polypoid organs seated upon it. Within this cavity is 

 usually sheathed a second conical capsule, traversed by the common 

 tube or " chapelet," and having also its air-bladder : in this the ovary 

 or testis is developed. As it enjoys independent movement when 

 separated from the former, it was regarded by Cuvier as a distinct 

 individual, developed by gemmation ; and it is homologous with the 

 medusoid individuals similarly developed, and appropriated to the 

 generative function, by ova, in the Coryne. The canal into which 

 the stomach ojjens terminates in a long rounded cavity, lined by a 

 ciliated epithelium. 



Two genera of physograde Acalephre have an elliptic or circular 

 discoid body, supported by an internal cartilaginous or subcalcareoua 



N 



