12 THE HYDROIDA IN GENERAL. 



In 1S3P Ehrenberg employs the term Bri/ozoa in a sense exactly equivalent to that of 

 Thompson's Poli/zoa, and in 1833" we find him proposing a new classitication of the heterogeneous 

 and unscientific grouj) of the " Polypi," by dividing them into the AntJiozoa, which embraced the 

 coelenterate forms, and the Bryozoa to which all the moUuscoid forms were referred. 



In the same memoir Ehrenberg also forms a separate group for the fixed Hydrozoa, which, 

 under the name of " Zoocoralia oligactinia," he separates from the Actinozoa. He further gives 

 a synopsis of such genera and species as were then known, and makes some valuable reforms in 

 the limitation and arrangement of the genera ; but the most important point in which this memoir 

 has advanced our knowledge of the Hydroida will be found in the ascription of an independent 

 zooidal significance to the so-called " egg-capsules" of these animals, and the consequent deter- 

 mination of a distinct sexuality among the zooids which compose a hydroid colony. This capital 

 discovery, whose true import, hovvevei', was but partially comprehended by Ehrenberg, has in the 

 hands of subsequent investigators undergone further development, and must be viewed as the 

 starting-point for all those more recent researches which have so largely contributed to bring 

 about the philosophical views now entertained regarding the structure, physiology, and 

 systematic position of the Hydro in a. 



In 1834 De Blainville published his 'Manuel d'Actinologie.'' The important reforms of 

 Eschscholtz, Rapp, and Ehrenberg are not adopted by De Blainville ; and the ' Manuel 

 d'Actinologie,' except in so far as it constituted a useful work of reference and description for the 

 student, cannot be regarded as in any way advancing the systematic arrangement, or aiding in a 

 philosophic conception of the Hydroida. 



The notes and drawings of Medusae made by Mertens during his voyage rovmd the world 

 as naturalist to the Russian exploring ship " Seniavin," were, after Mertens' death, entrusted 

 to Brandt, who has given us an account of them in two important memoirs. The first, published 

 in 1838,* consists in a synopsis of the genera and species observed by Mertens, among which are 

 several new genera of both hydroid Medusae and Discophora proper ; while in the second* he 

 gives us a more detailed account of them, and now publishes the numerous and beautiful figures 

 made by Mertens from the living animals. Brandt does not adopt Eschscholtz's division of the 

 Medusae, so that the hydroid Medusae are here mixed up with the Discophora proper. He gives 

 us detailed anatomical descriptions of the Medusae, so far as their structure was at that time 

 known ; but the chief value of the labours of Mertens and Brandt will be found in their rendering 

 us acquainted with new forms, and in their giving us the most beautiful and accurate figures of 

 Medusae which had been up to that time published. 



not printed on the title-page, but it will be found on the paper wrapper in which the publication was 

 originally issued. 



' Chr. Gdfr. Ehrenberg, ' Symbols Physicse,' iv, Berolini, 1831. 



" Corallenthiere. 



^ Henri Marie Ducrotay de Blainville, ' Manuel d'Actinologie ou de Zoophytes,' Paris, 1834. 



* J. F. Brandt, " Prodromus descriptionis Animalium ab H. Mertensio in Orbis Terrarum cir- 

 cumnavigatione obscrvatorum." ' Recueil des Actes de la Seance publique de 1' Academic Imperials 

 des Sciences de St. Petersbourg,' 1833-31. 



* Ibid. " Ausfiihrliche Beschreibung der von C. H. Mertens auf seiner Weltumsegelung beo- 

 bachteteu Schirmquallen," ' Mem. de I'Acad. Imper. des Sciences de St. Petersbourg,' vi ser., Sci. 

 Nat., tom, ii, Petersbourg, 1838. 



