;86 THE ANIMAL KINGDOM. 



as well. Sexual individuals of this species occur in autumn half to 

 a quarter the normal size, i. e. four inches. 



The characters above given apply to the second division of Acraspeda, 

 the Ephyroniae of Haeckel. A large number of Medusae belong to it, and 

 it contains three orders, the Cannostomae, Semostomae, and Rhizostomae. 



The first division of Acraspeda, the Tesseroniae, contains relatively 

 few forms. The bell is of great depth ; and in the Depastridae and 

 Lucernaridae it is produced into a hollow peduncle by which the animal 

 attaches itself at will. Its cavity is prolonged aborally into four interradial 

 4 funnel cavities ' of variable extent, corresponding to the four sides of the 

 manubrium. The angles of the latter are consequently attached by four 

 perradial septa, ' mesogonia,' to the subumbrellar wall. Rhopalia are ab- 

 sent in the Stauromedusae and their place may be taken in Lucernaridae 

 by adhesive tentacles, sometimes lost, or by simple tentacles in Tes- 

 seridae. They are four in number when present, interradial in Pero- 

 medusae, perradial in Cubomedusae. They bear one or two dorsal eyes 

 in the former, sometimes also a ventral : in the Cubomedusan Charybdaea 

 marsupialis three pairs, a large central and two lateral pairs. In the last- 

 named the retinal layer is cup-shaped ; the cup filled by a vitreous 

 body, to which is added in each of the large eyes a lens formed by elongate 

 ectoderm cells much as in Vertebrata. Charybdaea has also a continuous 

 nerve-ring, in position corresponding to the inner nerve ring of Craspedota. 

 It consists of fibres and ganglion cells, the latter especially aggregated at 

 the bases of the rhopalia, with an overlying ectoderm of sense and support- 

 ing cells. Tentacles are usually limited in number, and are rarely solid. 

 In the fixed forms they are capitate, ranged round the bell-margin in 

 Depastridae^ grouped at the end of eight short hollow adradial arms in 

 Lucernaridae. The mouth is square. The main gastric cavity consists of 

 four pouches communicating peripherally by apertures of varying size, 

 depending on the length of the septa that separate them 1 . Processes from 

 the cavity pass into the marginal lobes of Peromedusae, and the velarium, 

 when present, of Cubomedusae^ e.g. in Charybdaea. The taeniolae are greatly 



1 Claus points out (Untersuchungen, p. 14) that the starting-point of the Tesseroniae is con- 

 ceivably the stage in the formation of the Ephyra from the Scyphostoma at which the taeniolae are 

 perforated by passages putting the four gastric pouches into communication. The gastric cavity 

 becomes much complicated in the Peromedusae : see Haeckel, System, p. 402 et seqq. There 

 seems to be some confusion as to the character of the septa dividing the gastric pouches. In 

 Charybdaea marsupialis each septum is traversed by a layer of endoderm cells, showing that there 

 has been a fusion of the two walls of the gastric cavity. On the contrary, the septa of Lucernaridae, 

 as may be seen from Claus' figures (Untersuchungen, PL IX. Fig. 62 ; PL X. Figs. 71, 72), contain 

 no such layer, and are probably taeniolar growths. The distinction is certainly one of importance. 

 Haeckel appears to think that the septa in question, whether nodes, lines or lamellae, are always 

 formed in the same way: see Deep-sea Medusae, Challenger Reports, iv. pp. Ixix.-lxx. 



The Depastridae and Lucernaridae are probably to be regarded as specialised Scyphostomae, and 

 as standing apart from other Acraspeda. 



