DEVELOPMENT OF CYANEA CAPILLATA. 



117 



the base, each segment as it becomes detached presenting the form, 

 characters, and attributes of a free Acaleph, and in this condition as- 

 suming an independent existence, under the appearance represented in 



fig. 55, 17, a. 



Fig. 55. 



ir* 



Transformation from the polypoid form to the third, or Acaleph, condition (after Sars). 16. The 

 polypoid larva (16 a, natural size) in a more advanced state, now divided into segments piled upon 

 each other, each of which is a young Medusa, having its disk surrounded with radiating processes 

 bifurcated at their extremities. These segments becoming detached one by one from the summit 

 of the pile successively, assume the medusiform condition. 17. Another example, in progress of 

 division, in which only four segments remain undetached, and of these the three uppermost are at 

 the point of separation. 17 a. A segment of the preceding detached, now become a free Acaleph : 

 it is represented as seen from below, and already exhibits in its centre the square oral orifice, 

 round which are perceptible rudimentary tentacula, together with the radiating nutritive canals, 

 &c. 18. The same, in a still more advanced stage, exhibiting the rudiments of marginal tentacula. 

 19. The same, arrived at its perfect form, furnished with its four buccal arms, now completely di- 

 vided and pendent, and fully provided with the marginal tentacles of the adult. 



(305.) The now free Acaleph, the disk of which is not as yet much 

 more than i-th of an inch in diameter, exhibits, when magnified, the 

 characteristic organization of a true Medusa, the oral orifice (fig. 56, a), 

 the positions of the ovaria 6, the radiating nutritive canals, c, the 

 circular marginal vessels, d, the oculiform points, e, the anal aper- 

 tures, /, and the rudimentary tentacula surrounding the disk, g g, being 

 all easily recognizable. The Medusa being thus far complete, its 

 further advance is rapid, the rays become gradually shorter in propor- 

 tion to the disk, the marginal tentacles are more and more developed, 

 and at length the young Acaleph, complete in all its parts (fig. 55, 19), 

 will in time, by the production of multitudinous ova, give birth to 

 another generation, destined, during their development, to exhibit a 

 parallel series of changes. 



(306.) In some of the Medusa3 which are destitute of a central pe- 

 dicle, such as Cuvieria carisochroma (fig. 57), the arrangement, both of 

 the alimentary and generative apparatus, is considerably modified. In 

 ^Equorea violacea, examined by Milne-Edwards*, the gastric cavity, 

 which is very large, occupies nearly a third of the whole diameter of 

 * Ann. des Sci. Nat. for 1841. 



