KEPORT ON THE DEEE-SEA MEDUSAE. 5 



protoplasm, lie in their centre (fig. 5 d), and distinctly form a connected axial cord in the 

 centre of the whole column of cells (which in the solid oral styles of other Margelidae, as 

 in the similar tentacles of the Narcomedusse and many hydroids, were erroneously con- 

 sidered by former observers to be a " central canal "). This solid endodermal cellular 

 axis is surrounded by a thin, but firm and very elastic, strongly refringent, supporting 

 lamella, by whose elasticity the extension of the contracted oral styles is effected on the 

 cessation of the contraction of the muscle (figs. 5-7, z). The muscles, which in a great 

 measure shorten and at the same time thicken the oral styles by their contraction, form a 

 thin lamella, composed of longitudinal, parallel fibres. This muscular plate, here as in the 

 tentacles, is a product of the ectoderm, whilst the elastic lamella is secreted by the endoderm. 

 The ectoderm covering of the oral styles consists of flat epithelial cells which partly form 

 flagellate capsules, partly stinging capsules, and also contain numerous granules of blood- 

 red pigment. The stinging cells of the end knobs are not pigmented. 



The oesophagus or " gullet," which may also be termed " proboscis," and which springs 

 from the oral opening of the central gastral pyramid in the centre between the four stems 

 of the oral styles, is two or three times as long as the gastral pyramid, and projects far 

 beyond the velar opening of the umbrella cavity. It is quadrangularly prismatic, of equal 

 thickness in the two upper thirds, whilst the lowest third is swollen into an egg-shaped 

 pharynx without muscles. The latter is divided from the lowest part of the oesophagus, 

 which bears the quadratic oral opening, by a circular constriction (' c strictura palatina ") 

 (fig. 4). The thickened oral edge bears a circle of stinging knobs (figs. 4, an). The 

 four perradial corners of the oesophagus project strongly, whilst the concave lateral sur- 

 faces lie in folds. 



Order II. LEPTOMEDUS^E, Hseckel, 1866. 



Craspedota partly without, partly with marginal vesicles, these, when present, developed 

 from the insertion of the velum, with ectodermal otolite cells. Ocelli at the bases of the 

 tentacles sometimes present, sometimes wanting. Genitalia always in the course of the 

 radial canals. Number of the radial canals varying, sometimes four, six, or eight, sometimes 

 very large, sixteen, thirty-two, eighty, or even several hundred. Velum thin and delicate. 

 Ontogenesis, usually alternation of generations, often with metamorphosis. The 

 trophosome of the asexual generation is a hydroid-polyp of the order Campanulariae. 



Family, Cannotid^e, Hseckel, 1877. 



Caxnotid/E, Hseckel, System der Medusen, 1879, p. HO, taf. ix. 



Leptomedusse without marginal vesicles, with four or six radial canals, which are 

 branched, forked, or pinnated, in whose course the genitalia lie. 



