562 L. R. CRAWSHAY. 



failing, like others previously referred to, in consequence of high and 

 irregular temperatures at the time in this position. 



General. As bearing on the sensitiveness of some Calanoids to sudden 

 changes in the water conditions, the following example is important. 

 O21 June 15th, two Calcmus finmarchicus were given to me by Mr. Fuchs in 

 a large jar (brefht) of 2000 c.c. in capacity, in " outside " water contain- 

 ing a growth of Nitzschia, in which he had reared some Echinoplutei. 

 The culture had been started by him on April 19th, and kept from that 

 date on one of the slate slabs in the General Laboratory. In the water 

 that was used the two Calanus had been introduced unobserved, evidently 

 as young forms, possibly as nauplii, and these, feeding on the Nitzschia 

 culture, had grown to nearly full size. On June 15th the jar was taken 

 over by me and placed in Position A, where the Calanus continued 

 healthy until July 9th. The NitzscJiia having then grown too thick the 

 Calanus were transferred to a new culture in Berkefeld water, in a clean 

 jar. One specimen was stunned by the change, and fell to the bottom, 

 remaining almost motionless afterwards, and both died within two days. 

 The temperatures had been taken, and Mr. Matthews having kindly 

 analysed samples of the water and ascertained the densities, the change 

 of conditions from one jar to the other proved to have been as follows : — 



T. S.% <,, 



Jar A. "Outside" water 16-5 35-22 25-82 

 JarB. Berkefeld „ 17-5 37-94 27-68 



The temperature change being one of only 1°, it seemed evident that 

 the death of these Calanus was to be attributed to a sudden change of 

 2-72 in salinity, and owing to this the Berkefeld water subsequently 

 used in the experiments was diluted with 5% distilled water. It was 

 thought that by thus obviating such sudden changes in salinity, much 

 of the difficulty previously encountered in the experiments might be 

 overcome. It was not realised till later that repeated changes in the 

 air temperature communicating themselves less suddenly to the water in 

 the exposed vessels might be equally harmful in their effects. 



iSpecial Experiment in Position A. 



In the latter part of the year, it became increasingly evident that some 

 factor which had escaped observation was a constant source of harm to 

 the animals. In view of the possibility that this might be the presence 

 of Bacteria, several experiments, which will be referred to in detail 

 later, had been made in keeping Copepoda in the presence of strong cul- 



