398 D. J. SCOURFIELD ON THE SWIMMING 



have been carried out carefully, the animal will not be found 

 to have been in any way injured by the treatment, and will 

 soon commence to swim for dear life — so it thinks, no doubt, but 

 if the cement is good, it does not budge a ya. Unfortunately the 

 great trouble with the method has been to find a really reliable 

 cement. It is evident that a cement for this purpose must be 

 very tenacious even in most minute quantities, that it must set 

 rapidly, that it must not be soluble in w^ater, but, on the contrary^ 

 must even set under water, and, most important of all, that it 

 must have no bad efifects upon the animals. I must frankly 

 admit that, after trying most of the ordinary micro-cements,. 

 I have not yet found one thoroughly satisfactory, but I have 

 obtained the best results with sealing-wax dissolved in alcohol. 

 This cement will hold many Cladocera quite well for periods 

 varying from a few minutes to half an hour or more, but it will 

 not hold Copepods longer than a few seconds to a minute or so. 

 I shall be very pleased to have any suggestions as to a good 

 cement for the purpose in view. 



To return to the question of the swimming habits of Daplmia, 

 etc. As stated above, the point to be settled was whether 

 Simocephalus and Scapholeheris really did swim upon their backs 

 because they beat their large antennae towards their ventral 

 margins. By experimenting with Simocephalus vetulus, on the 

 lines just explained, I soon found that my theory was untenable, 

 for it was easily observed that the current of water produced by 

 the normal movement of the antenn£e was not only not towards 

 the ventral margin, but was actually somewhat inclined towards 

 the back. (See Figs. 5, 6, and 7, in which the line ms represents 

 the direction of the stroke. The opposite direction sm necessarily 

 represents the resulting line of movement.) The direction of the 

 current produced by all the specimens examined— and the same 

 fact was afterwards observed in the case of Dap)hnia — was as 

 nearly as possible identical. No current in any other direction 

 was ever observed. I should be sorry to deny the possibility of 

 these animals using their antennae in other ways, but there seems 

 no doubt that each species has a practically constant direction of 

 stroke under ordinary circumstances. 



I next examined species of Daphnia in the same way, and found 

 that the direction of the stroke was practically identical with that 

 of Simocephalus — i.e., that it was inclined obliquely backwards- 



