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



therefore, as in all Craspedotee, the sexual products originate from the ectoderm, 

 whilst the reverse is the case in the Acraspedotse, where, in both sexes, they are 

 formed by the endoderm. The ripe spermatozoa and the ripe ova are therefore thrown 

 outside immediately in the Craspedotse or " Cryptocarpse," whilst in the Acraspedse 

 or " Phanerocarpge " they first pass into the gastrovascular system, and are then ejected 

 by the oral opening ; the former are therefore properly " Ectocarpae," the latter 

 "Entocarpa?" (Hertwig, 1879). When Eschscholtz, the meritorious founder of the 

 system of the Medusa?, 1829, distinguished the two principal divisions of this class as 

 " Cryptocarpse " and " Phanerocarpse " according to the different formation of their repro- 

 ductive organs, he expressed prophetically an important difference, whose peculiar 

 character was first more accurately recognised fifty years later. 



Class II. ACRASPEDSE, Gegenbaur, 1856. 



Phanerocarpge, Eschscholtz, 1829. Steganophtaljle, Forhes, 1848. 



ScyphomeduszE, Ray-Lankester, 1877. Phacellotje, Ha;ckel, 1878. 



Medusae with gastral filaments or phacellas ; with endodermal genitalia (or sexual 

 products from the internal germinal layer) ; without true velum (often with velarium) ; 

 with true marginal lobes of the umbrella; without double centralised nerve ring. Phylo- 

 genetic descent (probably universal) and ontogenetic descent (at present still in the 

 majority) derived from scyphopolyps with gastral filaments or from scyphostoma. 

 Ontogenesis usually alternation of generations (in the form of strobilogenesis) often 

 connected with metamorphosis. The sexual acraspede generation is formed by terminal 

 gemmation from the asexual scyphostoma generation. 



Order V. STAUROMEDUS^, Haeckel, 1877. 



Acraspedaa without sense clubs, with simple tentacles or marginal anchors (adhesive 

 tentacle rudiments). Originally eight principal tentacles (sometimes rudimentary). 



Besides these eight principal tentacles there are often small secondary tentacles 

 (usually in bunches upon eight adradial marginal lobes). Stomach having four wide 

 perradial gastral pouches, which are separated by four narrow interradial septa or fused 

 selvages, and connected on the umbrella margin by a circular sinus. Genitalia, 

 four interradial horseshoe-shaped swellings or four pair of adradial swellings, which are 

 developed in the subumbral wall of the gastral pouches from their endoderm, and project 

 wholly or partially into their cavity. 



