CASSIOPEA XAMACHANA. 229 



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

 parently the oesophagus, as well as the gastric pouches, is lined with endoderm. On 

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

 ectoderm. 



The four radial tentacles are formed simultaneously, and the four interradial ones 

 appear at the same time or slightly later. These are followed by eight adradinl 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 other, thus agreeing with the observations of Glaus on Aurelia 

 and Cotylorhiza. 



The four gastric pouches are formed at the same time by the ingrowth of the septa. 

 They are soon brought into communication at the periphery by the perforation of the 

 septa, which become reduced to columellae surrounding the longitudinal muscles. 



Contrary to Goette's opinion, it may be staled positively that the rhopalia are differ- 

 entiated in the bases of alternate tentacles. After the rhopalium 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, Claus, and 

 Lendenfeld are fully confirmed. 



The scyphomedusae are the only coelente rates, which possess four longitudinal 

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

 insertion. The buds of Cassiopea have this distinctively medusoid characteristic long 

 before they are detached. Moreover, the methods by which the mouth and the gastric 

 pouches are formed differ entirely from what is said to take place in larvae that pass 

 through an anthozoan stage. Therefore, whatever may be true of the larvae derived from 

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



The first step toward the formation of the free-swimming medusa is the perforation 

 of the gastric septa which takes place in the young scyphistoma before it is fully 

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

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

 tion of the sense organs and the development of the marginal lobes of the umbrella, the 

 most important events are the development of the angles of the mouth into quadrate 

 lobes and the fusion of the two layers of endoderm along certain areas of adhesion so as 

 to divide the periphery of the digestive tract into a series of radial canals. Only one 

 medusa is formed ; but, separated from this by a constriction, is a small basal segment 

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

 tentacles, and a proboscis. This becomes eventually a perfect scyphistoma, and after a 

 period of growth probably undergoes stabilization again. 



