REPORT ON THE DEEP-SEA MEDUSAE. 



vn 



§ 4. Craspedotae and Acraspedae (System, p. xxiv. 1, 3G1). The class of the Medusae is 

 divided into two different sections or sub-classes, Craspedotse and Acraspedae. Both sub- 

 classes form natural principal groups, differing essentially and thoroughly from one 

 another in important conditions of organisation. Although single groups in both sections 

 are so like that they may be confounded together, and, in fact, have often been so, yet 

 the two principal groups differ fundamentally, and have probably arisen cmite independ- 

 ently of one another from two different groups of polyps ; their most important 

 differences are best seen from the following tables: — 



I. CRASPEDOTiB 01' HyDROMEDUSJE. 



A. Gastral space, without gastral filaments or pha- 



celli (Aphaeelhe). 



B. Genitalia ectodermal (sexual products of the outer 



germinal layer) (Cryptocarpa?). 



C. Umbrella margin with true velum, without true 



marginal lobes (Craspedotae). 



D. Organs of sense usually simple, without protec- 



tive plate (Gymnophthalmse). 



E. Marginal nerve ring double and centralised 



(Cycloneurce). 



F. Descent from Hydropolyps, or Polyps without 



gastral tseniola (Hydroniedusse). 



II. ACRASPED.E or ScYPHOMEDUSiE. 



A. Gastral space with gastral filaments or phacelli 



(Phacellotse). 



B. Genitalia endodermal (sexual products of the 



inner germinal layer) (Phanerocarpre). 



C. Umbrella margin without true velum, with true 



marginal lobes (Acraspedae). 



D. Organs of sense usually composite, with special 



protective plate (Steganophthalmae). 



E. Marginal nerve ring simple, usually non-central- 



ised (Toponeurae). 



F. Descent from Scyphopolyps, or Polyps with gas- 



tral taeniola (Scyphomedusae). 



§ 5. Hydropolyps and Scyphopolyps. The two sections of the class Medusae corre- 

 spond to two different sections of the Poly]) class, Hydropolyps and Scyphopolyps. The 

 lower more simply constructed Hydropolyps have retained a perfectly simple gastral 

 space with smooth inner surface (primitive intestine or "archigaster" of the Gastrcea). The 

 higher and more perfect Scyphopolyps are distinguished from the Hydropolyps by four in- 

 terradial longitudinal swellings or gastral ridges ("taeniola") being developed on the inner 

 surface of the gastral cavity, by which their peripheric part is consequently divided into 

 four broad perradial niches or pouches (" antra gastralia "). The Hydromedusae or 

 Craspedotae, as well as the classes of Siphonophorae, and Ctenophorae derived from them, 

 are descended from the Hydropolyps (Hydra, Clava, &c.) ; the gastral filaments are want- 



