Chap. I. STRUCTURE OF THE DISCOPHOR.E. 5 



distinct pouches communicating directly Avith the main cavity of the body and 

 discharging their eggs into that cavity and then througli the mouth ; while in the 

 CryptocarpjB they consist only of folds along the course of the chymiferous tubes or 

 upon the sides of the proboscis, and discharging their eggs immediately into the 

 surrounding medium, Ijut never through the main cavity and the mouth. Here, 

 then, is a typical difference between two natural groups of the Discophorte of former 

 authors; and it is upon this ground that I would separate the PhanerocarpsB from 

 the Cryptocarpoe as a distinct order, especially since I shall be able to show that 

 while the latter differ in this way from the former, they at the same time agree 

 both in structure and in mode of development with the Hydroids and SiphonophortB, 

 and should form with them another distinct order. 



The discoveries respecting the mode of development of the Acalephs made during 

 the last quarter of the present century add great weight to this distinction, for they 

 show that while the Phanerocarpa? produce, either directly or through the process of 

 a transverse division of a polypoid young, a kind of larva (the Ephyra), which 

 is gradually transformed into a perfect Medusa, the Cryptocarpas originate in alternate 

 generations as buds from similar polypoid animals. But even if nothing was known 

 of the mode of reproduction of the Discophora) Phanerocarpas and Cryptocarpoe, I 

 maintain that these Acalephs, in their adult state, should be separated from one 

 another on account of their structure. 



The body of the Cryptocarpas consists of a disk, of an umbrella or bell-shaped 

 form, the lower layer of Avhich, perforated in the centre, projects from the lower 

 surfoce in the shape of a longer or shorter proboscis, terminating in various ways 

 in different families. The two layers recede slightly from one another at the base 

 of the proboscis, and form a more or less extensive central cavity, from which 

 arise directly a larger or smaller number of narrow tubes extending to the edge 

 of the disk, where they are vmited by a similar continuous, simple, circular tube, 

 beyond which the margin of the disk is bent inw'ard in the shape of a j^rojecting 

 veil, more or less closing the space beneath the disk ; while from the border, 

 formed by this inversion of the margin, arise, along the circular tube, a larger or 

 smaller number of plain or hollow tentacles, in some families limited to the point 

 of intersection of the radiating and circular tubes, and in others extending around 

 the whole disk. Pigment specks appear upon the base of the tentacles of some; 

 while in others, more comj)licated eye-specks or auditive vesicles occuj)y the position 

 of tentacles. 



In the Phanerocarpje, on the contrary, the lower layer of the disk not only 

 recedes from the upper, but thickens around the central opening into four solid 

 pillars supporting the four angles of the digestive cavity and extending downward, 

 in the shape of four so-called arms which surround the mouth. This peculiar structure. 



