28 Proceedlings 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 
days, the lobes of the rotatory organ and the general structure 
