8 THE IIYDROIDA IN GENERAL. 



with the trophosomc, and has described the radiating canals and the included ova of this body 

 in his Scrfidaria pennaria (Pennaria disfi/c/ia, Goldfuss), without, however, exactly compre- 

 hending its true significance or its relations to a free hydroid Medusa. He also insisted on the 

 vegetality of the proper corallines or nullipores, which, on the estabhshment of the animality of 

 corals, were carried with these into the animal kingdom. The results of his researches were 

 published in 1785, in a work' full of valuable information, and illustrated with excellent figures 

 of living hydroids, corals, and Polyzoa. 



In the ' Elenchns Zoophytorinn ' of Pallas, published in 17C6, all the known hydroid 

 trophosomes were distributed among three genera — Hydra, Tnbnlaria, and Sertidaria. In the 

 ' Spicilegia' Pallas adds the genus Coryne from Gaertner MS. Gmelin, in his edition of the 

 ' Systema Naturae,' 1788, while he overlooks the genus Coryne, adds the new genus Clava. 

 Besides these different genera of hydroids, all characterised from their tro])hosomes, several true 

 hydroid Medusae had been at this date known and described; but they were all included along 

 with steganophthalmic forms, and with Siplionophora and Ctenophora, under the common generic 

 name of " JNIedusa," given to them by Linnaeus. 



The state of the natural history of the Hydroida at the date of the publication of the 

 thirteenth edition of the ' Systema Naturae' (Gmelin's) may thus be stated in a few words : — The 

 animality of the Hydroida was fully acknowledged. Such species as were known by their 

 trophosomes were distributed under five genera — Hydra, Tubularia, Sertularia, Coryne, and 

 Clava, while such free gonophores as were known were thrown together with all the other free 

 forms of Hydro~oa under the common name of Mediim. 



The natural history of the Hydroida, which during the latter half of the eighteenth century 

 had been thus steadily advancing in the hands of Trembley, Jussieu, Ellis, Pallas, Forskal, O. P. 

 Midler, and Cavolini, was, with the commencement of the nineteenth century, destined to receive 

 a fresh impulse. 



The famous voyage of Peron and Lesueur inaugurates the natural history labours of the 

 nineteenth century. It was commenced in 1800, and in 1S04 the voyagers returned laden with 

 new and important facts for science. No expedition could have afforded better opportunities of 

 studying the pelagic forms of invertebrate animals ; and soon after their return Peron and 

 Lesueur undertook a systematic description of the Medusce which they had obser\'ed in the great 

 seas which their ships had traversed, as well as of other species which they had studied in expeditions 

 afterwards made to the coasts of Normandy and to the Mediterranean. In the two memoirs^ in 

 which they pulilish the results of their researches they propose an entirely new classification of the 

 Medusa3. The old Linnean genus Medusa is broken up into numerous separate genera, and 



' Filipo Cavolini, ' !Mcmorie per scrvir alia storia dc Polypi Marini.' Naples, 1785. Translated 

 in 1813 into German by Sprengel. 



" ' Voyage de Decouvertes aux Terres Australes, fait par ordre du Gouvernement sur les cor- 

 vettes " le Geographe," " le Naturalists," et la goelette " la Casuarina," pendant les annees 1800 a 1804, 

 redige par Peron et continue par M. Louis de Freycinet,' 2'' edit, revue, corrigee, et augmentee, par 

 M. de Freycinet. Paris, 1824, 1825. 



^ Peron et Lesueur, " Notions preliminaires sur les Meduses," ' Ann. du Museum,' 1809, 

 p. 218; and 'Tableau des Caracteres generiqucs et specifiques de toutes les Especes de Meduses 

 conuues jusqu'a ce jour,' id., p. 325. The plates referred to all through the second memoir have, 

 unfortunately, never been published. 



