1908] 



Davis. Life-history of Doliclwglossus. 



193 



Period II in D. pusillus is a time of active swimming, and 

 varies in length from twelve to twenty-four hours as shown in 

 observation of twelve individuals. Intervals of rest occur, during 

 the period, and these become longer as the larva grows older. 

 When swimming actively the larva appears much like a miniature 

 tornaria, both in outline and relative length of longer and shorter 

 axes. However, the similarity goes further than this. Like tor- 

 naria it swims chiefly from below upward. It may occasionally 

 take a horizontal course, but this is always undulatory and never 

 in a straight line. Like tornaria, its swimming movements are 

 produced by the cilia of the ciliary band. Like tornaria, also, it 

 does not swim vertically upward but takes a spiral course, the 

 direction of the spiral, as in tornaria, being clockwise. 



Unlike tornaria, as far as has been observed, it has a regular 

 cycle of movements which is repeated at rather regular intervals. 

 Beginning at the bottom it swims vertically upward always 

 describing a spiral. When near the surface of the water the 

 direction becomes horizontal and the path undulatory instead of 

 spiral; then the animal ceases to swim and falls rapidly to the 

 bottom. The bottom having been reached, after a short period 

 of rest, the cycle- of movements is repeated. Sometimes a new 

 cycle may begin before the bottom is reached. 



The following is a tabulation of a typical series of swimming 

 cycles : 



