50 J. M. D. OLMSTED 



ments on each. The species used were Planocera caUfornica, 

 Phylloplana littoricola, and Leptoplana saxicola. The species 

 were determined by means of the key and descriptions given by 

 Heath and McGregor ('12). 



The worms could be kept for an indefinite time in fingerbowls 

 in the laboratory, provided the water had been taken directly 

 from the bay, and there was present a small amount of a green 

 alga, such as ulva. No food was provided, although judging from 

 the color of the digestive tract some of the green alga was in- 

 gested, for the intestines of specimens in dishes without the alga 

 never showed a greenish tinge. The temperature was about 

 15°C. 



In making the more careful operations, the worms were ren- 

 dered motionless by adding crystals of chloretone to the sea- 

 water, but since all except P. californica very frequently disin- 

 tegrated in the chloretone solution (cf. Heath and McGregor, '12), 

 the majority of operations were performed without anaesthe- 

 tizing. This disintegration while the worms are still living is a 

 most striking phenomenon. All the cells, epithelial, muscle, 

 digestive, separate from each other and the cytoplasm liquefies, 

 leaving free nuclei, pigment granules, etc. The result is a mass 

 of slime which clings to the dish when one attempts to remove 

 the animal. This disintegration takes place first in the posterior 

 half of the body in the region of the digestive tract. Occasionally 

 this part will entirely drop out, leaving the margins intact except 

 at the tip of the tail. The second region to disintegrate is that 

 immediately anterior to the brain. Figure 1 indicates the posi- 

 tion of these two regions. 



It was found that all three species regenerated in the same 

 manner, and, with the exception of P. californica, in approxi- 

 mately the same time. P. californica is much larger than any of 

 the other species, its tissue is much firmer, and regeneration pro- 

 ceeds much more slowly. The lengths of time given below for the 

 regeneration of various parts refer to P. littoricola and L. saxicola. 



After cutting these polyclads in two by a transverse section 

 anywhere posterior to the cephalic ganglia, the anterior piece 

 restored all the missing parts. New material was evident along 



