441 W. DE MORGAN AND THE LATE G. HAROLD DREW. 



the finger-bowls in troughs of running water in order to keep them cool 

 and at a more or less constant temperature ; before this was done a 

 very large mortality among the restitution masses occurred even under 

 the most favourable conditions, and it would seem that the temperature 

 of the laboratory, which is heated by hot water, was too high for these 

 unless some artificial method of coohng was employed. 



Two kinds of water were used in the experiments : (1) that brought 

 from outside the Plymouth Breakwater, and (2) water circulating in 

 the Laboratory tanks, treated with animal charcoal and passed through 

 a Berkefeld filter as described by Allen and Nelson (see Journal of Marine 

 Biological Association, Yo\. VIII, p. 455 ). It proved, however, immaterial 

 which kind of water was used. For the first day or two the water of the 

 cultures was changed frequently with a view to keep down the infusoria 

 and flagellates as much as possible ; but it is impossible to banish them 

 altogether, and as soon as a perisarc was well established round the 

 masses they were immune to attacks of protozoa. After this time the 

 culture water was not changed oftener than once a week. Possibly the 

 flagellates developed more quickly in the Berkefeld than in the outside 

 water. 



It was found advisable to utilize the colonies of Antennularia im- 

 mediately after they were brought in, as by this means more vigorous 

 restitution masses were obtained. If the colonies were kept over night 

 in the ordinary tank water, in the filtered Berkefeld water, in water col- 

 lected from outside the Breakwater, satisfactory results were not ob- 

 tained. In one experiment, however, excellent results were obtained 

 from a colony of A. antennina, which had lain for some weeks in a labora- 

 tory tank. The comparative greater longevity and vitahty under 

 Laboratory conditions of the restitution masses compared to the original 

 colonies is very curious and difficult to explain. 



The changes in shape and other general external developments of 

 the restitution masses were noted by frequently drawing under a camera 

 lucida : for this purpose the watch-glasses containing the cultures were 

 simply removed from the finger-bowls and placed on the stage of the 

 microscope ; after drawing they were returned to the finger-bowls with- 

 out disturbing the cultures. 



When required for histological examination, the restitution masses 

 were fixed in Flemming's fluid (strong formula). Ten minutes fixation 

 was found to be long enough for a moderate sized mass, say about the 

 size of a grain of barley ; if fixed for longer periods the cells showed a 

 tendency to become " osmicated " and stained badly. After fixing they 



