92 THE MEDUSAE. 



in the ectoderm in other regions as well ; but it is only over the stomach 

 and canals that the ectoderm layer is thick enough for them to produce 

 a visible color. I have been unable to find any pigment granules in the 

 endoderm. 



Pegantha smaragdina, like Cunina prohoscidea, as already stated, exhibits 

 an alternation of generations of medusae, our smaller specimen showing 

 an almost complete series of stages in the development of the secondary 

 generation. These will be described in detail in the ensuing pages. For 

 the sake of completing the systematic description of the species I must, even 

 at the cost of repetition, insert here an account of its most advanced stage. 

 The oldest medusae of this secondary generation were ready for independent 

 existence, and were taken in the same haul with their parent-host. They 

 measure about 3 mm. in diameter and are very flat. An aboral view of one 

 is shown in PI. 26, fig. 5. Their most important structural feature is that 

 they lack canal system and otoporpae. There are from ten to twelve ten- 

 tacles and from one to three otocysts per marginal lappet. The lappets are 

 short and broad, the incisions between them hardly marked. The stomach 

 is a simple circular sac. A section of the oral gastric wall (PI. 24, fig. 7) 

 shows that it already consists of many layers of densely crowded ectoderm 

 cells, — a fact which suggests an early formation of sexual products, such as 

 takes place in the corresponding generation of Cunina prohoscidea, as described 

 by both Metschnikoff ('86*) and Stchelkanowzew (: 06). Apparently the sex 

 cells are developed generally over the stomach surface — a fact which, taken 

 together with the absence of gastric pockets, canals, and otoporpae, would 

 throw the specimens into the genus Solmaris, were their parentage not 

 known. 



The only described species of Pegantha at all approaching P. smaragdina 

 in either size or number of tentacles is P. magnifica Haeckel, which is 50 mm. 

 in diameter, with thirty tentacles ; but the two species are so sharply sepa- 

 rated by form, shape of the marginal lappets, conformation of the gonads, 

 and number of otocysts (Haeckel, '79, p. 333, records 900-1000 of these 

 organs for P. magnifica) that there can be no question that they are distinct. It 

 is perhaps possible that P. smaragdina may be identical with the specimen de- 

 scribed by Brandt ('38, p. 364, taf. 7) from Mertens's figures as Pohjxenia 

 flavibrachia ; but since his figures show neither canals, stomach, gonads, nor 

 sense organs, it is absolutely impossible to tell definitely even the family 

 to which this form belongs. 



