8 DESCRIPTIVE CATALOGUE OF THE 



divided by a deep fissure into two secondary lobes, which are generally 

 pointed. During these changes the groove has deepened until only a slender 

 peduncle connects the young medusa, formed in this way, with the rest of the 

 body of the strabila. This peduncle finally breaks off, and the young star- 

 shaped medusa, which is termed an " Ephyra," swins away, and by gradual 

 changes attains the structure of the adult jelly-fish. 



The Ephyra is a small and thin star-shaped disc, measuring 1.5-3 mm. in 

 diameter. The margin is regularly divided into eight or sixteen primary, and 

 sixteen or thirty-two secondary lobes. The centre of the disc is occupied by 

 the gastral cavity, which is lens-shaped, and from which a radial canal leads 

 into each of the primary lobes. From the lower side a short quadrangular 

 tube is suspended, which surrounds the mouth, situated at its base. The 

 mouth is extended in the four primary radius, which being vertical on each 

 other, give the mouth the peculiar shape of a cross. At the terminations of 

 the eight or sixteen primary radial canals, and situated in the depressions 

 between the secondary lobes, the marginal sense organs are found. These 

 consist of a conic body, the smaller end pointing outward, and contain a 

 number of crystalloid bodies in their distal entremity, the otoliths. They are 

 hollow. The cavity is clothed with entoderm, and communicates with the 

 primary radial canals. 



Gastral filaments make their appearance in the Interradii on the lower side 

 of the stomach. 



Histologically the Ephyra is nearly as highly developed as the adult. The 

 sexual organs are not yet formed, and the nerves, which radiate from the 

 marginal sense, organs, extend in the ectodermal epithelium instead of the 

 sub-epithelium as in the adult. 



It appears that not all the species of Scyphomedusre undergo this change of 

 generation. Pelagic species are developed from the invaginated gastrula 

 direct in as much as the gastrula never becomes sessil, and produces a great 

 amount of mesodermal gallert at an early stage, at the same time it attains 

 a flattened shape, forms a mouth, and is directly converted into an Ephyra. 

 Aurelia, although generally developing in the usual way by means of a 

 change of generations, may under certain circumstances develop direct 

 hypogenetically. Haeckel assumes that the Oubftmedusa?, the development 

 of which is unknown, may develop likewise in a hypogenetic manner without 

 change of generation. 



The Ephyra is converted into the adult Medusa by a process of simple 

 Metamorphosis. 



