40 THE VOYAGE OF H.M.S. CHALLENGER. 



cells. A low cudodermal fold, like that in Pedis (PL VI. fig. 12, yc), but less strongly- 

 developed, rises at the distal margin of the festoon canal, projecting freely into its 

 lumen (PL XII. fig. 12, yc). 



In contrast to the preceding Polycolpa, in which the reproductive glands appear in 

 their simplest form as a circular closed girdle in the lower wall of the stomach, 

 Pegantha shows us the most widely differentiated and highly developed form of the 

 genitalia. Here the originally simple and connected genital girdle is divided into a 

 circle of separate reproductive sacs, hanging freely in the periphery of the gastral 

 cavity. Each lobe cavity of the umbrella collar receives one genital pouch, which is 

 surrounded and protected by the concave subumbral surface of the collar lobes (PL XI. 

 fig. 3 ; PL XII. figs. 7, 9). The genera of the Peganthidse, Polyxenia and Pegasia 

 represent connective intermediate forms between the two extremes Polycolpa and 

 Pegantha, so that we have here the division of the simple subgastral reproductive 

 girdle into a circle of separate pouches, shown in four different phylogenetic stages 

 (comp. my System der Medusen, 1879, pp. 327-332). The cavities of the isolated 

 reproductive sacs of Pegantha pantheon (fig. 5, sc) communicate with the periphery 

 of the gastral cavity (figs. 7, 9, sc). Each of the eighteen genitalia has the shape of a 

 thick roundish leaf, with the two edges turned towards the edges of the collar lobes, 

 whilst the upper surface is delicately twisted or folded (fig. 3, s). The transverse section 

 (figs. 5, 6) shows that the gastral endodermal epithelium of the sac cavity (sd) is com- 

 posed of high cylindrical cells, and divided by a strong supporting plate from the mass 

 of the spermatozoa (sm). On the other hand, the latter is in continuous connection 

 with the gastral ectodermal epithelium of the subumbrella, from which it originates. 

 Under stronger magnifying power, we find the same condition here which Hertwig 

 described (1878) in Cunina lativentris. The superficial ectodermal layer of cells 

 (figs. 5, 6, sio), which forms the subumbral cover of the testes, sends out supporting- 

 fibres containing nuclei (zs) into the subepithelial layer of cells lying beneath it. The 

 larger cells of this layer (sm) usually lie inwards, touch the endodermal fulcral plate 

 (2), and must be regarded as " mother cells of the spermatozoa," whilst the smaller cells, 

 which usually lie outwards, form spermatozoa already ripe (fig. 6, sz). 



Family, jEginid^;, Gegenbaur, 1856. 



JSginid^:, Hasckel, System der Medusen, 1879, p. 334, taf. xix. fig. 8, 9; taf. xx. fig. 11-16. 



Narcomedusse with a marginal canal communicating- immediately with the stomach by 

 double peronial canals, with internemal gastral pouches (which have arisen from the 

 distal lobe pouches of radial canals through retrograde formation), without otoporpse or 

 auditory clasps at the basis of the auditory clubs. 



