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



IV. GASTEOVASCULAE SYSTEM OF THE MEDUSA. 



§ 97. Composition of the gastro vascular system. Of the two large organic systems 

 composing the body of the Medusa, the gastrovascular system includes the complex of 

 the vegetative organs, the apparatus for nutrition and reproduction, and is, therefore, 

 physiologically opposed to the neurodermal system, which forms the complex of the 

 animal organs. This antithesis is shown histologically in relation to the two primary 

 germinal layers, as the majority and more important parts of the gastrovascular system 

 originate from the endoderm (or " vegetative germinal layer "), whilst those of the neuro- 

 dermal system, on the contrary, originate more usually from the ectoderm (or " animal 

 germinal layer "). The apparatus of nutrition, formed by the principal intestine (stomach 

 along with the oral organs) and the radial coronal intestine proceeding from it (vascular 

 corona or pouch corona), is by far the more considerable and widely differentiated of the 

 two apparatuses composing the gastrovascular system. The apparatus of reproduction is 

 much simpler and less differentiated ; it consists solely of the sexual glands or genitalia, 

 which are developed in the subumbral wall of the gastrovascular system. 



§ 98. Hollow space and walls of the gastrovascular system. The entire gastrovascular 

 system of the Medusae, in spite of its numerous and important modifications in different 

 groups, shows everywhere one and the same essential type of formation. It appears 

 everywhere as a more highly developed formation of that simple gastral hollow space, 

 which is met with in the lowest polyps (Hydra, Clava, &c, among the Hydropolyps ; 

 Scyphostoma, Spongicola, &c, among the Scyphopolyps). The primitive, perfectly simple 

 gastral cavity of these oldest polyps is nothing more than the original primitive intestine 

 (" archigaster, archenteron ") of the gastrsea, which still forms the common ontogenetic 

 base for the intestinal system in the gastrula of all Metazoa ; its simple opening is the 

 primitive mouth (" archistoma, blastopores). We distinguish the two walls of this 

 primitive intestine of the polyps as the aboral calyx wall ("paries calycinalis, calyx") 

 and the oral peristomal wall (" paries peristomalis, peristomium ") ; the two pass 

 immediately the one into the other at the margin of the calyx (" margo calycinalis "). 

 In the Medusa?, the notumbrella corresponds to the calyx on the one hand and the 

 ccelumbrella to the peristomium on the other ; we, therefore, term the calyx wall of the 

 gastral space the dorsal wall (" paries umbralis " or " dorsalis ") and the opposite inner 

 or peristomial wall the ventral wall (" paries subumbralis " or " ventralis "). The 

 endodermal epithelium of the former is always formed of small flat flagellate cells, that 

 of the latter of large high flagellate cells (§ 47). 



§ 99. Principal intestine and coronal intestine (" axogaster et perogaster "). In all 

 Medusae the gastrovascular system or intestinal system is divided first of all into two 

 different principal sections, into a central and a peripheric part. For brevity we shall 

 term the former the principal intestine, and the latter the coronal intestine. The 



