Introduction to Animal Morphology. 



103 



free 



Two orders are included herein : 



i. Rhizostomida Reproductive organs in 

 zooids, with no marginal tentacles nor Fig. 14. 

 central mouth, but with a tree-like 

 mass depending from the umbrella, 

 bearing many, mouth-like openings, 

 formed by the irregular gaps produced 

 by the contact and adhesion of com- 

 plexly folded oral lobes. 



In this order, and the next, the Marginalbodvofchab y. 

 young embryo on emission from the ? n ^ a it?s?aik pl cavi't> s , h two 

 egg is a planula (Fig. 15, 3), which, a e n n d oneTithocyst bdw.' 

 after a short locomotive period, attaches itself by its 

 narrow end to some solid body, and forms a mouth 

 and stomach by invagination at its distal end, around 

 which four rudi- 

 mental tentacles 

 develop (15, c) ; 

 these elongate, and 

 others form in their 

 intervals. This 

 hydra-like form 

 lengthens, its 

 mouth extends into 

 a manubrium-like 

 process, and Ion- ,,?,- ';--' 

 gitudinal canals 

 sket* h from the mouth to the wall of the body. 



This trophosome having livd for a variable time 



(c.d.\ the elongated wall of the hydra tuba (as it is 



railed] becomes marked by a series of transverse 



annmd its rirrumference, which deepen, 



dividing the tube into a series of superposed discs, like 



'>, development nf Auri-lia aurita, 



tub. i ; </. H \ilr.i tuli.i budding; 



, Strobila; .C, Kphvra : /, tentacles; 

 ; ( . < . i ii.-ul.ir < .inal. 



