78 ACALEPHJE. 



which are likewise capable of spontaneous elongation. When not 

 in use, these organs are retracted within the body, and lodged in 

 two membranous sheaths visible in the drawing, from which they 

 are protruded at the pleasure of the animal, and, as they expand, 

 gradually uncurl the spiral, secondary tentacula by movements 

 which are singularly graceful and elegant. 



In Medusa aurita there are seen around the circumference of 

 the locomotive disc certain red spots, which Ehrenberg regards as 

 eyes, without however adducing the slightest proof that they 

 possess any claims, derived either from their structure or function, 

 to the name which he is pleased to give them. 



(106.) Most anatomists have failed to detect nervous filaments 

 even in the largest medusae ; nevertheless Ehrenberg is inclined to 

 believe that in some Pulmonigrade species a delicate thread, which 

 encircles the margin of the disc, is to be regarded as nervous, as 

 well as others, which he describes as being visible around the base 

 of the pedicle. In the Beroe (Cydippe) pileus, (Jig. &2) Pro- 

 fessor Grant* regards a double cord which runs around the oral 

 extremity of the alimentary canal, of which an isolated view is 

 given at Jig. %%, 2, as constituting the nervous system ; this ar- 

 rangement, however, has not been confirmed by later observations, 

 and we are inclined to think that the vascular circle which sur- 

 rounds the mouth ( 102) of the Beroeform species has been in 

 this case mistaken for nervous fibre. 



(J 07.) We know little satisfactorily concerning the mode of gene- 

 ration in the acalephse, the opinions of authors upon this subject 

 being in the last degree vague and contradictory. Confining our- 

 selves to the examples which have been selected as best adapted to 

 put the reader in possession of the principal facts known concerning 

 the class under consideration, we find the organs usually regarded 

 as the agents of reproduction assuming very different forms. In 

 Cassiopea Borbonica, the parts which Delle Chiaje describes as 

 ovaria, are four membranous tubes filled with granular matter, and 

 placed above the stomach (Jig. 28, c) ; from each of these a canal 

 issues, which, dividing into several smaller branches, opens by as 

 many minute orifices into four cavities placed around the stomach, 

 into which the sea-water is freely admitted. 



According to Gaede*^ and Eysenhardt,j the ovaria examined 



* Transactions of the Zoological Society, vol. i. 



f Beytrage zur Anatomic und Physiologic der Medusen. Berlin, 1816. 8vo. 

 J Zur Anatomic und Naturgeschichte der Quallen j Rhizostoma Cuvierii. Mem. de 

 1' Academic Leopold des cur. de la Nature. 



