28 Proceedings of the Royal Physical Society. 



addition to the length of the spiral ribbon, and that with the 

 increasing age of the animal the number of spiral turns would 

 continually increase. Such, however, is not the case, as I 

 shall proceed to show. 



Mode of Reproduction in Lagotia. 



As I was anxious to ascertain the mode of reproduction in 

 Lagotia, I was kindly allowed to take away with me several 

 of the stones from the aquarium. These were placed in a 

 large glass vessel of sea-water, and careful daily search was 

 made for some weeks to discover larvse, but without success, 

 although young Lagotias were beginning to attach themselves 

 to the sides of the glass. At last, I discovered several dark 

 green specks swimming in the water : these were caught one 

 by one, placed in large flat cells, and covered by bell-glasses, 

 to prevent evaporation, where they became developed into 

 Lagotias. 



The young of Lagotia producta, in its earliest stage 

 (fig. 4), is a short cylindrical body, with rounded extremities 

 of a dark sea-green colour. The surface of the body is marked 

 by coarse striae, each of which carries a fringe of long lashing 

 cilia, by the aid of which the animal urges itself rapidly 

 through the water, at the same time rotating on its axis. It 

 quickly assumes a more lengthened form (fig. 5), the ante- 

 rior extremity of the cylinder puts forth a fringe of long cilia, 

 and the posterior extremity becomes pointed, while the cilia 

 of the body become much diminished in size. ' A number of 

 young at this stage were placed in the flat cells, and were 

 found the next morning to have attached themselves to the 

 surface of the water as to a solid substance, and to have de- 

 veloped their tubes with all the spiral rings complete, the 

 imbrication of the rings being even more marked than in the 

 adult specimens. The rudiments of the bilobed rotatory organ 

 had also appeared (fig. 6) ; while the cilia of the body had 

 still further decreased in size, although the striated texture 

 of the surface was still strongly marked, and formed a beau- 

 tiful object under strong microscopic power. In three or four 

 day3, the lobes of the rotatory organ and the general structure 



