ON OTENOPLANA. oe 
say, in what would correspond to the transverse plane. This, 
however, is quite wrong. 
As will be seen later on, I agree with Korotneff in his iden- 
tification of the antero-posterior axis (in comparison with 
bilateral animals), but it is along this axis that the solid 
tentacles lie. 
Furthermore, Korotneff’s specimen did not give him an 
exhibition of its swimming powers, so that he could not 
observe the movements of the ctenophoral plates, and the 
result was that he formed the opinion that these plates had 
become altered as to their function, and that they hardly 
appeared to serve for the progression of the body. This 
is a curious repetition of the old error with regard to the 
means of locomotion of the Ctenophores, as set forth in 
Chun’s monograph. As a matter of fact, when Cteno- 
plana swims, the ctenophoral plates are its sole means of 
locomotion. 
I now pass on to a systematic account of my own observa- 
tions. 
1. Shape and Movements of the Body.—Like the 
Planarians, the body of Ctenoplana comprises a thickened 
median ridge-like area and two lateral thin skirt-like areas, 
the “Seitenfelder” of Lang. In the attitude assumed when 
crawling, the body is nearly round with the exception of 
the above-mentioned marginal bays, from which I observed 
the muscular pinnate tentacles being constaxtly protruded and 
retracted while the animal was crawling (fig. 1). As also 
observed by Korotneff, Ctenoplana crawls with one of the 
rounded margins of the body directed forwards as a rule. The 
tentacles thus appear remarkably like transversely paired 
structures, and one would naturally at first describe them as 
such. But it must be remembered that the terms anterior, 
posterior, and transverse, as applied to bilateral animals, 
are not applicable to Ctenoplana. 
The tentacles, when extruded, are found to be white struc- 
tures, thus making a marked contrast to the green or red 
colour of the body. They are provided with small secondary 
VOL, 39, PART 3.—NEW SER. Y 
