46 JAMES Francis ABBort, 
so extended may measure 5 or 6 cm across in longest diameter, 
shrinking to one-fifth that diameter when contracted. 
1. Life habits. 
Coeloplana cannot swim, either as a ctenophore, or by means of 
the flattened skirt of the body, as some planarians do. I have never 
found it floating, but in the quiet of the aquarium it usually came 
to the top and spread itself out, adhering to the surface of the 
water by the ventral face of the body, as a planarian. In this 
habit of floating it seems to resemble WiLLEy’s Ctenoplana. At such 
times Coeloplana, especially ©. mitsukurii, throws out its long delicate 
tentacles which hang down in the water and wave about in very 
oraceful fashion, and then the great length of the tentacles in 
comparison with the size of the body is made apparent (Fig. 2). 
If disturbed when so floating, — either by the water being agitated 
or by the body being touched by a foreign substance, — it falls to 
the bottom in a shapeless lump. Wıuuey describes his Ctenoplana 
as folding together like a book under such circumstances, but there 
is no such axis of flexure in Coeloplana. If dropped, dorsal side 
uppermost, it rights itself without difficulty. Many experiments and 
observations were made to ascertain whether the animal crawled in 
any one direction rather than in another, and it was proved con- 
clusively that it did not. The act of crawling seems to be wholly 
a response to peripheral stimuli and as such stimuli may act on 
two or more sides at once, we have the remarkable spectacle of 
two sides of the animal progressing in different directions. As noted 
by Kowazevsky this mode of progression is, in a sense, amoeboid. 
A projection of the body is pushed out and the rest of the body 
tissue behind it, follows on. When the animal is crawling, the whole 
periphery of the body is thrown into folds and outpushings. This 
is especially to be noted in the red form, ©. willeyi, where no con- 
sistent body shape is maintained and where different sections of the 
body may overlap each other. One result of such a habit is that 
the internal structures become twisted about so as to defy orientation. 
When the animal is very active it will often, while crawling, throw 
out the tentacles in a cloud of white filaments. The whole mass of 
filaments seems to be expelled at once and then to be slowly 
withdrawn. The ejection of the tentacles is effected by a sudden 
contraction of the muscular walls of the sheath. The two tentacles 
