IO4 Introduction to Animal Morphology. 



a pile of saucers. In this "scyphistoma" stage, the 

 segments become more and more separable, each 

 saucer becoming lobate round its margin, and then 

 the column is called a strobila (/) ; finally, each 

 separates as a free swimming disc or ephyra (g\ which 

 by degrees assumes its adult form, swims by the contrac- 

 tions of its umbrella, and develops ova and spermatozoa 

 in its genital pouches. The young free zooids ofRhizos- 

 tomidse have a single central mouth (Brandt\ but as the 

 oral lobes increase in the complexity of their folds, and 

 as these folds irregularly cohere, they produce the irre- 

 gular polystomous, oral lobes, characteristic of the adult 

 (stoDiatodoidrci). A degree of bilateral symmetry 

 may be noticed in some Rhizostomidae, and clavate 

 tentacles are scattered upon the oral lobes. The 

 bases of the stomatodendra unite into a syndendrium^ 

 attached by four stout processes or dcndrostyles to the 

 under surface of the umbrella, between which are the 

 genital pouches. 



The order Rhizostomida includes six families : 

 i. Rhizostomidae with four genital pouches, opening by as 

 many sub-genital pores ; eyeclusters eight, four in the meri- 

 dians of the arm-roots (per-radial), and four inter-radial ; 

 stomatodendra much curled, leaf like, forming sucking 

 combs, ex. Rhizostoma, Mastigias, &c. 2. Leptobrachidse 

 with four genital pouches, and four sub-genital pores ; single, 

 thin, unbranched stomatodendra, without tentacles, with one 

 tuft of border-plaits and suckers, ex. Leptobrachia. 3. Cas- 

 siopeiidae with eight genital pouches, and sub-genital pores; 

 eight ocelli ; no tentacles ; arms forming an eight-rayed 

 rosette, of dendritic tufts ; ex. Cassiopeia, Crossotoma, &c. 4. 

 Polyclonidae with four genital pouches, and sub-genital pores ; 

 stomatodendra long, continuously dichotomously twigged ; 

 no long tentacles ; twelve ocelli, four per-radial, and one on 

 each side of each of these (ad-radial), ex. Polyclonia, Sala- 



