22C> T;r)i'.F.r>T I'ayne r.rcKLow ox 



niJirjfiii. 'I'll*' deepest lolils mi'c the most dist.-il. iiikI lliev liecoine [iroH-ressively more 

 slialliiw towMi'il tli<' liase of the arm. The central month is still widelv open. The snhu'eni- 

 tal eaxilies aic well developed at this stage. Fiii's. ()4, (iO, and (Ki show liow the oral disc 

 is lorme(l, and how the snhgenilal cavities are prodneed li\ the great increase in tiiickiies.s 

 of the mesouloea at the pillars of the pi'ohoscis and the liases of the oral arms. l?y the 

 o'vowtli of these strnetnres. the snliu'eiiital caNilies are necessai'ih' iirodnced. The oid\' 

 Special adaptations are the subsequent growth and folding of the ahoral wall and the 

 narrowing of the orifice. 



The marginal lohes of the mnhrcdla now hegin to hi'oaden. and thns approach the 

 adnlt condition. Imt there is (ndy a single " \'ellar " lohe between two rIio]ialial ones. 



At a little later stage, when there ai'e three oral iinmels at the tips of the arms 

 (Fig. 33), the re-enti-ant angles between the pillars of the proiioscis have grown inward, 

 met at the centre, and fnsed. Tn this way the bnni'n of the oesophagns is divided 

 into fonr tnbes (Fig. ^l'.!). representing the grooves that were present in its angles in the 

 earlier stages. in the lignre the fusion at the centre has g(>n<> so far as to invoh'e the 

 edges of the lips, ami the labial grooves of the dil'fei-ent pairs of arms ait- not in o])en 

 commnnication. but a short cross-shaped tube connects them at the centre, and the oral 

 disc is now com[ilcted. 



It is interesting to note that Clans has found a stage both in I'ilema and in Coty- 

 hu'lii/.a that, while showing the cliaracteristic fannly difierences, has also a certain 

 resemblance to this stage in Oassiopea. In all three the walls t\\' the proboscis have fnsed 

 so as to di\ide its lunu'u into four tnbes, and the formation of oscnla has lieguu at the tips 

 of the arms in snch a way that we have on each arm three oscula with a vesicle in the 

 ano-les between them. The occin-rence of this staux- in the ontooenv of three so dislin<-llv 

 separated families must have some morphological signiiicaiK-e. ami we niay regard these 

 eight primal}' xi'sicles as homologous in the three gron[is. 



The mode of formation of the oral funnels hecomes (>\ident at this stage. They are 

 not fornieil in (Jassiopea simply by a series of fusions of the lips along the line ol the 

 lal)ial groove, as llamann (81) states to be the casein Cotylorhi/.a. It is more like the 

 process in Pilema, as described b\- Clans. Each of the piimary funnels is represented at 

 lirst by one of the folds in the mai'giu of the lips referred to above (F'ig. 33) . The 

 folil di'e|iens. and its edges are brought together on the \cntral side and fuse. lea\iug an 

 o|iening at the a,])e.x of tlie fold, the osculum. At the same time the lal)ia,l groove in 

 this region is converted into a canal b\- the fusion of the lips on its two sides. After 

 the fusion all trace of what has occurred (piickly disappears. 



With the division of the oesophagus into four tubes, and the completion ol the oral 

 disc, our larva comes to be distinctly a rhizostoniatous medu.sa. Further development of 



