• CASSIOPEA XAJNIACHANA. 229 



tho formation of the mouth there is no evidence of any invagination of ectoderm Ap- 

 parently- the oesopliagus, as \vell a.s the gastric pouches, is hned with endoderni. On 

 the other hand, the oesophagus of the lower disc of the strobila is formed wholly of 

 ect(i<lcrui. 



Tile four radial tentacles are foriui'd simultaneously, and the I'oiu- interradial ones 

 appear at tlu' same time or slightly later. These are followed by eight adradial tentacles 

 and sixteen more are added a little later, making thirty-two in all. It was found that the 

 rudiments of the interradial tentacles are not at all constant in position with relation 

 to the septa. Some were septal, others were interseptal, sometimes on one side of the 

 septum, sometimes on the otlier, thus agreeing with the observations of Clans on Aurelia 

 and Cot} lorhiza. 



The foui' gastric pouches are loiined at the same time by the ingrowth of the septa. 

 They are soon brought into comnuniication at the periphery by the perforati(m of the 

 sejita. which beconu- reduced to colnmellae surrounding the longitudinal muscles. 



Contrary to Goette's o]iiuion, it may be stated positively that the rhopalia are differ- 

 entiated in the bases of alternate tentacK's. After the rho^ialiuiu is fully developed, the 

 distal part of the tentacle undergoes degeneration and is absorbed. The development was 

 traced for the first time through all its stages, and the opinions of Agassiz, Clans, and 

 Lendenfeld are fully conliriued. 



The sc_\ phomcdusae are the only coeleuterates, wiiich possess four longitudinal 

 muscles of ectodermal origin completely imbedded in the mesogloea between the points of 

 inserti(ui. The buds ol Cassiopea have this distinctively medusoid characteristic long 

 before the_y are detached, Mort'over. the methods by which the mouth and the gastric 

 pouches are formed dilTer entirely fiom what is said to take place in larvae that pass 

 through an autho/.oan stage. Therefore, whatever ma}' be trvie of the larvae derived from 

 eggs, this stage is certainly omitted in larvae produced by budding. 



The fh-st step toward the formation of the free-swinuuing medusa is the perforation 

 of the gastric septa which takes place in the young scyphistoma l)efore it is fully 

 developed. Then follows a period of growth and reproduction by buihling, and further 

 uietaniorjihosis begins finally with the process of strobilization. Besides the differentia- 

 tion of till' sense organs and the de\ elo[)nient of the marginal lobes of the umbrella, the 

 most important events are the de\elopnienl oi the angles of the mouth into ([uadrate 

 lolies and the iusiou ol the two layiMs ot eudodcrm along certain areas of adhesion so as 

 to divide the periphery of the digestive tract into a series of radial canals. ()ul\' one 

 medusa is formed ; but, separated from this by a constriction, is a small iiasal sc'^ment 

 which, a short time before the medusa becomes free, begins to develop gastric pouches, 

 tentacles, and a [iroboscis. This becomes eventually a perfect scyphistoma, and after a 

 period of growth probably uuilergoes strobilization again. 



