CASSIOPEA XAMACUANA. 227 



the mouth parts consists in the continued division of the labial, or brachial, grooves into 

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

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

 the centre of the oral disc. Except for this interruption, the development of the mouth 

 parts proceeds regularly in a centripetal direction. The funnels and vesicles are formed 

 lirst at the tips of the arms, and then one after another in regular succession toward the 

 centre. Each of these primary funnels is the rudiment of one of the primary branches of 

 the arm. When the process of forming funnels has reached about half the length of the 

 arm, the distal funnels begin to subdivide. By this subdivision of the primary funnels 

 new ones are produced, of which some are the rudiments of secondary branches ; these sub- 

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

 but takes place in such a way as to produce alternate branches. The formation of a 

 vesicle takes place at this stage in some way at about- the time of the completion of the 

 adjoining funnel. I have not been able to determine whether the vesicle is a funnel with 

 (lie orifice closed, as Ilamanu claims it to be, or whether it is an evagination from the 

 pedicle of a funnel, as at first it seemed to me to be, and as Glaus thinks it probably is. 



According to Haeekel ('79), the genus Archirhiza represents a form that was the 

 ancestor of all the rhizostomatous medusae. Of this genus there are two known species, 

 A. primordiafis Haeekel, and A. miroxa Haeekel. They agree in having four subgenital 

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

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

 representing this condition is a feature of the ontogeny of rhizostomatous medusae. From 

 what has been said it is evident that we have no such stage in the development of Cassi- 

 opea xamachana, for while the labial groove is still open in the proximal half of the oral 

 arm, in its distal half the vericles are formed, and branches are in the process of 

 formation. 



The outline of the umbrellar margin has not changed essentially since the last stage. 

 The areas of adhesion have become much wider than the radial canals they separate, and 

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

 have become numerous. 



We have now followed the larva of our Cassiopea from its first appearance as a bud 

 to a point where, with the exception of the gonads, all the organs of the adult are out- 

 lined. Here we must take leave of it. 



