4 THE HYDROIDA IN GENERAL. 



We have no evidence whatever to show that the Greek and Roman naturahsts were 

 acquainted with any member of the Hydroida. Aristotle and the naturahsts of Greece and 

 Rome who followed him had some knowledge of corals, sea-anemones, and steganophthalmic 

 Medusa; ; but this was very imperfect, while no mention is made by them of a single hydroid, and 

 it is not until the eighteenth century that we find in the writings of naturalists anything beyond the 

 most obscure indications of an acquaintance with the animals now included in the order Hydroida. 



It was in the beginning of the eighteenth century that the fresh-water Hydra was discovered 

 by Leeuwenhoeck, and its faculty of buddhig like a plant accurately described. Leeuwenhoeck 

 communicated a notice of this discovery to the Royal Society of London in 1803.' 



The first grand impulse, however, to the study of the Hydroida was given some years later 

 by Trembley. Abraham Trembley was born in Geneva in 1700, and in 1743 was awarded the 

 Copley medal by the Royal Society of London, of which he had been elected a Fellow. It was 

 while residing at the Hague with his two pupils, the sons of the Count de Bentinck, that he 

 obtained, in the pond at Sorgvliet, the coimtry house of the count, the hydras which enabled 

 him to make that remarkable series of observations on the reproductive powers of these animals 

 which resulted in the discovery of jjhenomena hitherto unsuspected in the animal kingdom, 

 and of the highest significance in physiology ; for they established the fact that the animal 

 organism may not only midtiply itself by budding in the manner of a plant, as Leeuwenhoeck 

 had already demonstrated, but that it may possess the power of enduring repeated subdivision, 

 and may suffer with impunity the most extensive mutilations, the fragments of the divided Hydra 

 not only recovering from the operation, but becoming endowed, after a time, with all the parts of 

 which they had been deprived by the act of division. 



The discoveries of Trembley were communicated to Reaumur, and recorded by him, in 1742, 

 in the preface to the sixth volume of his ' History of Insects;'" and in 1744 an extended account 

 of them was published by Trembley himself, in his celebrated treatise on ' Fresh-water Polypes.'' 

 In this remarkable work the species of Hydra known to Trembley are described with copious 

 details of their general structure and habits, and of the curious experiments to which he subjected 

 them. The work consists of four memoirs, and is abundantly illustrated with figures of great 

 beauty exhibiting the Hydra in various conditions and under various modes of treatment, all 

 from the pencil and most of them from the graver of the celebrated Lyonet ; while the quaint but 

 expressive vignettes from another hand, which are placed at the heads of the four memoirs, and 

 which represent various parts of the grounds of Sorgvliet, with the author and his two pupils 

 engaged in the capture and observation of the Hydras, give an additional charm to a work which 

 must be regarded as the most important step yet made towards a scientific knowledge of the 

 Hydroida. 



The progress of discovery in the natural history of the Hydroida, however, is so intimately 



connected with various observations which had been about this period made on certain corals 



and other Actinozoa, that it is impossible to follow the one without some knowledge of the other. 



The researches of Trembley were preceded by Peysonelle's demonstration of the true nature 



of the polypes of coral. The coral polypes were discovered towards the beginning of the last 



^ Ant. de Leeuwenhoeck in ' Phil. Trans.' for 180.3. 



- Rene-Antoine Ferchaud de Reaumur, ' Histoire des Insectes.' Paris, 1743. 

 ' 'Memoires pour servir il I'Histoire d'un genre de Polypes d'eau douce il bas en forme de 

 Comes.' Leyden, 1744. 



