454 



THE ZOOLOGIST. 



is usually in such water. This examination enables the move- 

 ments of the Eotifers to be seen under sufficiently fair and 

 natural conditions. Since, however, the bdelloid Eotifers will 

 usually be burrowing in or becoming entangled with the sedi- 

 ment on the slide, it will be, in most cases, practically impossible 

 to examine their anatomical features advantageously. To do 

 this the Eotifers should next be transferred by one or more 

 pipette operations to a little distilled or very clear water, so that 

 finally there is no particle of sediment present. If, owing to the 

 vigorous movements of the Eotifers, it becomes necessary to 

 narcotize them, this should be done cautiously so as not to pro- 

 duce too violent a contraction. With this precaution the Eotifers 

 often recover somewhat, especially if a little pure water is added 

 on the slide, and finally move about sufficiently slowly to enable 

 their anatomical features to be examined. A compressor is 

 useful, but so far I have had no need to use it. Another point 

 is worth mentioning. It never seems to be worth while to spend 

 much time in examining inferior specimens of a species. Eotifers 

 are very small animals, but, like much larger ones, they seem to 

 present great differences in vigour and development. Some of 

 them show to the fullest extent the peculiarities of the species, 

 as regards size, form and movements. The 

 examination of such specimens with every care 

 always repays for the time spent on them. 



The Eotifer, P. citrina, under consideration, 

 exemplifies some of the above remarks. Although 

 not a common species in the country of the 

 Chess and Gade, it is occasionally found in the 

 pools, especially those of Chipperfield Common 

 and Langleybury, and in the little streams near 

 the canal, as well as the canal itself. Alto- 

 gether a score or more specimens had been 

 examined at various times, but it was not until 

 July 14th, 1914, that an exceptionally good 

 specimen, both as regards form and colour, was 

 obtained. This, the only one procured on that 

 date, was from the canal at Boxmoor. Further, 

 there happened to be only a small quantity of 

 sediment in the water, and examination of the Eotifer was 



Fijj. 17. 



