120 SUPPLEMENT 



has seen a nais, whose intestine was filled with Daphnise still 

 living, which it had taken very dexterously when swimming. 

 Their mode of generation is pretty nearly unknown. It is 

 said, however, that they are oviparous, and that towards 

 spring, is perceptible, towards the two thirds of the length of 

 their body, and underneath, an elongated mass of a different 

 colour from the intestine, and which, seen through the micro- 

 scope, appeared to contain an innumerable quantity of eggs. 

 This is to be seen for a longer or shorter time, which depends 

 upon the heat of the season ; but in general it has disappeared 

 at the commencement of summer. The na'ides can be mul- 

 tiplied artificially, by cutting their body transversely into 

 many pieces. Such, at least, was the result of the experi- 

 ments of Trembley and of Roesel ; M. Bosc, however, tells us 

 that he has repeated them without success. 



The ancients appear to have been acquainted only with the 

 most common species of HiRUDO, and these animals were 

 not yet employed in medicine, at the time of Hippocrates. 

 Pliny designates them very well under the name of Hirtt- 

 dines, and of SanguisugtB, distinguishing two species. Many 

 new species have been added in modem times, and they have 

 been divided into generic groups. Many scientific men have 

 studied their organization, the knowledge of which yet ap- 

 pears hardly complete, if we may judge from the very great 

 and singular differences of opinion existing on many points of 

 consequence respecting it. 



A part of their history, which had been much neglected 

 until later times, but the study of which has been necessitated 

 by their dearness, and the difficulty of procuring them for 

 medicinal purposes, is their mode of reproduction and preser- 

 vation. M. Lenoble, a physician of Versailles, appears to be 

 the first who noticed that the medicinal leeches formed a sort 

 of cocoon, which Bergman had before observed in relation 



