CASSIOPEA XAMACHANA. 227 



tlu' moiitli |);irts consists in the ('mitiniied division of the labial, or l)rachial, grooves into 

 oral fnnnels and brachial canal, together with tlie development of oral vesicles. By the 

 time two or three vesicles have l)een formed on the end of each arm, a vesicle appears in 

 the (tenti'e ol tiie oral disc. Except for tiiis interrnption. tlie development of the mouth 

 parts proceeds regnlarlv in a centripetal direction. The funnels a,nd vesicles are formed 

 first at llic tips of the arms, and then one after anolhei' in regular succession towai'd the 

 centre. Each of these primary funnels is the rudiiiicnt of one of the priniar\' branches of 

 the arm. Whi-ii the ]irocess of forming funnels has I'cached al)ont half tiie length of the 

 arm, the distal funnels begin to snl>(li\i(lc. P>y this subdivision of tlie ])rimary funnels 

 new ones are produced, of wliidi some are the rudiments of secondarv branches ; these sub- 

 divide again, and so on. as long as growlli continues. The subdivision is not dichotomous, 

 liut takes [)lace in such a way as to pro(luce alternate branches. The formation of a 

 vesi(de takes place at this stage in some way at about the time of the completion of the 

 adjoining fnniu'l. I have not been able to ilelernnne whether the vesicle is a funnel with 

 the orifice clost'd, as llamann claims it to be, oi' whether it is an I'vagination from the 

 pedicle of a funnel, as at lirst it st'cmed to nu' to be, and as (Hans thinks it probably is. 



According to Ha.eckel ('79), the geiuis Archirhiza represents a form that was the 

 ancestor of all the rhi/ostomatous medusae. Of this genus there are two known s|)e(Mes, 

 A. prriiiorditi/is Ilaeckel, and .1. iiiimsti llaeckel. They agree in having foui- subgeuital 

 cavities and eight simple nnbr.niched arms that are provided with a single zig-zag row of 

 closely set oral funnels, and are devoid of other appendages. llamann says that a stage 

 re[iresenting this condition is a featm-e of the ontogeny of rhizostomatous medusae. From 

 Avhat has been said it is evident that we liave no .such stage in the develojmient of Cassi- 

 njtfd xdiiiiii-hdiiii. lor while the labial groo\e is still open in l!i<' jproximal half of tlie oral 

 arm, in its distal li.df the vericles are formed, and brandies are in the process of 

 foi'uialion. 



The outline of the undirellar maruin has not cluinced esseutialh since tlie last sta^e 

 The areas of adliesion have liecome much wider than the radial canals they separate, and 

 in them there has appeared a network of anastomosing canals, wliile the gastric filaments 

 have become numerous. 



We have now followed the lai-\;i of our Ca.s.siopea from its lirst appearance as a bud 

 to a point where, with the excei)lioii of the gonads, all the organs of the adult are out- 

 lined. Here we nuist take leave of it. 



