8 
THE ESSEX NATURALIST. 
nigra appear indifferent to the direction of running water. Poly- 
celis cornnta reacts only feebly. 
I 
Nutrition. The food of planarians consists of small 
crustaceans, insect larvae, small worms, and sometimes dead 
animals or even plants. The planarians discharge quantities 
of rhabdites which, when in the water, produce mucus, wherein 
the prey becomes entangled and is then devoured. A planarian 
is able to penetrate the joints of fresh-water amphipods and 
isopods by means of its muscular proboscis, although no signs of 
teeth can be detected. It is probable that a special secretion 
assists in this difficult process. When once the skin has been 
penetrated, the proboscis is inserted and ingestion commences. 
A recently-fed planarian usually shows the ramification of the 
intestinal lobes, owing to the presence of partly digested food. 
The undigested portion is returned through the mouth. (See 
P- 5 -) 
Planarians have a marvellous power of withstanding hunger, 
and they are able to live for months, and even for a year, without 
food. Stoppenbrink (37) has studied this subject carefully and 
he found that the size of the animal diminished steadily during 
starvation. Specimens of Planaria alpina, kept for nine months 
without food, had diminished almost to one-fourth of their original 
length. The sexual organs degenerated in the inverse order of 
their development, while the nervous, alimentary and excretory 
systems underwent little change. This is a somewhat unusual 
occurrence in nature—the immediate sacrifice of the race for the 
welfare of the individual. 
Reproduction and Regeneration. All fresh-water 
planarians are hermaphrodite, and under favourable conditions 
reproduce sexually by means of eggs, several of which are 
deposited in a cocoon. 
The time for cocoon production depends upon the species, 
and upon the temperature rather than the season. Generally 
speaking, however, Bdellocephala punctata, Planaria alpina and 
Polycelis cornuta are sexually mature during the winter and early 
spring; Planaria gonocephala and PL torva in summer and 
autumn. Bohmig (3) states that Dendrocoelum lacteum is a 
winter, and Polycelis nigra a summer, layer. I have found 
