NARRATIVE OF THE CRUISE. 
601 
sea as the Medusae, with their soft, gelatinous, watery bodies and their natatory life. 
There are, however, some few species of this class which descend to great depths. In 
the Memoir only eighteen such species are described, and in many of these cases it is 
very doubtful whether they are really inhabitants of the deep sea, or whether they 
have not been accidentally caught by the dredge while it was being drawn up to 
the surface. 
“Two families of peculiar Medusae can, with a considerable degree of certainty, be 
regarded as characteristic inhabitants of the deep sea, namely, the Pectyllidae among the 
Craspedota, and the Periphyllidse amongst the Acraspeda. 
“ The Pectyllidae (genera Pectis,Pectyllis, and Pectanthis ) belong to the order of Tracho- 
medusae ; they are nearly related to the Trachynemidae, and are especially remarkable 
for their peculiar suctorial tentacles, which are distributed in great numbers around the 
margin of the stiff almost cartilaginous umbrella (shown in the contracted state in fig. 200). 
These tentacles closely resemble the ambulacral tube-feet of the Echinodermata ; they are 
highly contractile and elastic, and are armed at the ends with a strong sucker. The 
living Pectyllid uses these for attaching itself, and also to creep with, just in the same 
Fig. 200 .— Pedis antarctica, Haeckel ; twice the natural size. 
manner as a starfish or a sea urchin. Another peculiarity of the P ecty llidse consists 
in eight radial “ Mesogonia ” or sexual mesenteries ; these are membranous septa in the 
hollow of the umbrella, which divide it into eight “ adradial ” partitions, and are extended 
between the subumbrella, on the one hand, and the eight gonades or sexual glands, which 
surround the basis of the stomach, on the other. 
“The Periphyllidse (represented by the two genera Periphylla and Periphema ) are 
Acraspedote Medusae of a very curious and complicated structure, and belong to the 
peculiar order Peromedusae, which was first constituted by Professor Haeckel in 1880, in 
his System der Medusen. They possess many important characteristics common to the 
Lucernaridae on the one hand, and to the Charybdeidae on the other. The highly arched 
and conical umbrella bears on its margin four interracial sense organs of very remarkable 
structure, and between these, twelve very long and powerful tentacles (four perradia 
