292 APPENDIX I 



(5) The small size of the whole animal also agrees with 

 the supposition. 



It is interesting to find that Packard's measurements for 

 L. glacialis (from Cape Krustenstern ?) make it even smaller 

 than the Spitzbergen variety. From this, however, it is 

 difficult to draw any certain conclusions, as his drawings 

 give a fully-developed tail-plate (see Monograph of the 

 North American Phyllopoda). It thus appears that L. 

 glacialis may be much stunted by unfavourable surroundings. 



That the specimens from Spitzbergen were not young 

 specimens follows from the facts that they (several hundred) 

 were nearly all the same size, and that they were caught in 

 the end of August, a week or so before the close of the short 

 summer, while the freshwater pools were still unfrozen. Pro- 

 fessor Kiikenthal informs me that this season in the latitude 

 in which they were found lasts about ten weeks. 



Packard's measurements for a fully developed L. glacialis 

 make it doubtful whether we are to look upon this variety 

 as permanent. It is possible that in favourable summers 

 they may further develop (without any great increase of 

 size) into stunted L. glacialis. This question, however, can 

 only be certainly answered by cultivating specimens further 

 south, in an aquarium, to see whether they develop into 

 L. glacialis. In the meantime it will be useful to call the 

 animal L. glacialis var. Spitzbergensis, or, for shortness, 

 L. Spitzbergensis. 



