bonnet's experiments on annelids. 63 



to be with tlieir motliers. The young one only lived four 

 Jays. 



This spontaneous self-division of worms is a curious fact, 

 first observed and accurately described by the Genevese 

 naturalist, Charles Bonnet,* whose discoveries in reproduc- 

 tion we shall have to consider in a subsequent Chapter. He 

 found the fresh-water Nais frequently double, and saw the 

 separation take place. He also cut the worm into several 

 pieces, and observed each piece reproduce its head, and grow 

 into a perfect worm. One observation he made is worth 

 repeating here.f He cut a Nais transversely, but not 

 entii-ely in two ; that is to say, the two portions were 

 held together by a mere thread ; in less than an hour after- 

 wards the tw^o were again perfectly united, and no trace 

 remained of the operation, except a slight constriction, and 

 an interruption in the continuity of the vessels and viscera. 

 This interruption was very similar to such as he had ob- 

 served in several worms in their ordinary condition ; and if 

 we compare the observation with that made by M. Peltier,^ 

 we shall see that they confirm each other. "In those 

 species," says M. Peltier, "which have a dorsal contractile 

 vessel, in which the course of the nutritive fluid can be 

 traced, we see that in proportion as the fluid becomes 

 poorer, the contraction becomes feebler, and is arrested 

 at the point where the fluid, having been already absorbed, 

 ceases to arrive. Here we see in the middle of the body, 

 at the very point where the nutritive fluid is arrested, a 



* BOXXET, Traiie (CI nsecioloijie, 174.5, vol. ii. t -^'""'^- ^^^- "• P- 133. 



+ See Comptes Rendus des Seances de I'Academie, 1844, Jan. 22, p. 161. 



