14 THE HYDROIDA IN GENERAL. 



Nearly at the same time some beautiful additional observations were made by Dujardin/ 

 who traced various known forms of free hydroid Medusa; to their fixed trophosoraes, and had 

 seen them produce eggs ; from this epoch we may regard as definitely established the genetic 

 relation between the free hydroid medusa and the fixed trophosorae. 



In 1843 two memoirs on the Campanularian and Tubularian Hydroids were presented by 

 Van Beneden to the Royal Academy of Brussels." The structure and gemmation of several 

 sj)ecies are described at length, and the memoirs are accompanied by very beautiful figures. 

 He has seen and described with much detail the free medusoid gonophores, as well as the fixed 

 sporosacs, but he mistakes the former for embryos destined by direct metamoqihosis to become 

 changed into the form of the polypoid trophosome. He founds the new genus, Hi/dractulia, for 

 the Alcyonium ecUnatmn, of Fleming, and calls attention to the polymorphism of the zooids in 

 this interesting and remarkable hydroid. 



The voyage of the French corvette, " La Coquille," under the command of Duperrey, during 

 the years 1822 — 1825,^ afforded to Lesson, who, along with Garnot, accompanied the 

 expedition as naturalist, fine opportunities for the study of the Medusae ; and in 1843 we find 

 him publishing, as a volume of the " Suites a Buffon," his 'Histoire Naturelle des Acalephes.'* 

 Lesson's work contains a great mass of information, and shows that its author must have had a 

 very extensive acquaintance with the Medusae, and yet we cannot say that, beyond the description 

 of some new forms, our knowledge of the Hydroida has received from him any advance. 

 Indeed, he does not avail himself as he might of the discoveries of his predecessors, while in his 

 classification the Hydroid medusas are, as usual, mixed up with the BiscopJiora proper. 



Up to this ])oint of our history it is plain that the systematic w^-iters who came after 

 Eschscholtz have fallen behind him in their appreciation of the Hydroid medusae as a natural 

 group ; for though Eschscholtz misunderstood the peculiarities of organization on which he 

 founded his "Discophora cryptocarpge," this group is not the less a natural one, and the 

 cryptocarjm of Eschscholtz must be recognised in every system which would aim at expressing 

 the true position and affinities of the various members of that large and heterogeneous assemblage 

 of organisms which have been included under the common name of Medusae. 



It was not, indeed, until 1846 that the Eschscholtzian division of the Medusa? into two 

 grand groups was distinctly accepted by any other naturalist. In this year, however, a paper 

 was read before the British Association by Edward Forbes,^ in which the author divides the 

 Medusae into two groups, corresponding with i\\e phanerocarpcB and cryptocarpm of Eschscholtz. 



The erroneousness of Eschscholtz's interpretation of the characters on which he founded his 

 subdivision had by this time become apparent, and Forbes accordingly, while admitting the 

 value of the groups, bases them on other characters than those employed by Eschscholtz ; for he 

 finds in the condition of the marginal bodies and of the gastro-vascular canals points of structure 



' Fel. Dujardin, "Observations sur un nouveau genre de Medusaires [Cladonema) proveuaiit de la 

 Metamorphose des Syncorynes," 'Ann. Sci. Nat.,' 2e ser., 1843. 



- P. J. Van Beneden, ' Recherches sur I'Embryogenie des Tubulaires, et I'Histoire Naturelle des 

 differents genres de eette famille qui habitent la cote d'Ostende,' Bruxelles, 1843. 



' 'Voyage autour du Monde sur la Corvette la Coquille, pendant les Anuees 1822, 1823, 1821 

 et 1825, par M. L. J. Duperrey, capitaine de fregate, commandant I'expedition.' 



^ Eene Primevere Lesson, ' Histoire Naturelle des Zoophytes. Acalephes.' Paris, 1843. 



•^ Edward Forbes, " On the Pulmograde Medusse of the British Seas," ' Brit. Assoc. Rep.' for 1846. 



