DEVELOPMKNT OF LOST PAKTS IN THE NEMEBTEANS. 251 



Note on the Development of Lost Parts in the Nemerteans. ' 

 By W. C, M'Intosh, M.D., E.L.S. 



(Plate VII.) 



[Read June 18, 1868.] 



The investigator of the Annelids is familiar enough with in- 

 stances of the reproduction of lost parts throughout the entire 

 series, and it is almost unnecessary now to refute the hasty as- 

 sertions of our countryman Dr. Williams, especially in those 

 worms experimented with by Spallanzani, Bonnet, Morren, and 

 others. No definite remarks, however, have ever been made, so 

 far as the author is aware, with respect to the same power in the 

 Nemerteans. 



In a paper on the structure of the British Nemerteans * the 

 author has described the reproduction of the proboscis, the 

 growth of an amputated anterior end (often consisting of little 

 more than a head) into a perfect body and tail, and the remark- 

 able tenacity of life enjoyed by many of the dissevered fragments 

 of the body, which survive for months and elaborate the genera- 

 tive elements in their interior ; but since these remarks were 

 made, it has been found that, at least in one species, each of the 

 numerous fragments into which its lengthened and fragile body 

 breaks becomes a perfect animal. Thus has nature gifted these soft 

 worms with a wonderful power of resisting destruction, both as 

 regards the abundance of ova and the vitality of rejected frag- 

 ments : their very softness and fragility only aid their multipli- 

 cation. 



In retaining specimens of Borlasia octoculata, Johnst., in con- 

 finement, they have often a great tendency to rupture them- 

 selves into many pieces. These fragments lie on the bottom of 

 the vessel, and, in the majority, consist of the body-wall, its 

 nerve-cords and vessels, the central alimentary chamber, and the 

 dorsal sheath for the proboscis. Numerous parasitic gregarini- 

 form bodies, as well as the peculiar ova formerly described f, 

 may also be seen in them ; and the new animal is thus supplied, 

 ab initio, with such structures in its digestive tract without 

 being subjected to the minor stages in their development. For 

 some time after separation the large aperture of the digestive 



* Lately comrnunicatocl to (he Eoyal Society of Edinburgh, 

 f Journ. of Micros. Science, 1867. 



