ZOOLOGY AND DOT ANY, MICROSCOPY, ETC. 451 



* Some points in the structure of an Anabffina.' The material was taken 

 from the main tank in the Victoria Regia House at Kew, and was at : 

 first intended for the study of an QCdogonium, but a month or two later 

 that alga had almost entirely disappeared from the glass vessel, and 

 was superseded by a rich growth of blue-green algae. The species of 

 Anabcena here considered occurred in all stages of development, and was 

 remarkable for the abundant heterocysts. These were not much larger 

 than the ordinary vegetative cells, and sometimes were even smaller. 

 They developed from the vegetative cells, and were generally to be re- 

 cognised at a very early stage. Two kinds were to be distinguished : 

 terminal ones, of a spherical shape, flattened on the sides towards the 

 vegetative cells ; and intercalary ones, more or less barrel-shaped and 

 flattened at each end. The structure and development of these hetero- 

 oysts is described, and the author remarks that his account scarcely 

 agrees with Brand's observations on Nostoc commune and Tolypothrix . 

 In young filaments the heterocysts occur singly and at considerable 

 intervals from one another, but in older filaments the author has seen 

 ;is many as four heterocysts side by side at one extremity of a filament, 

 the distal one being often the most fully differentiated. Various re- 

 agents were tried on these bodies, and the respective results are described. 

 The presence of cyanophycin-granules has been demonstrated in the 

 vegetative cells of the young filament, and in older filaments it is noticed 

 that they disappear from the vegetative cells and are found in the 

 heterocysts. A protoplasmic communication is shown to exist between 

 the heterocysts and the adjacent vegetative cells, and it is supposed that 

 the cyanophycin-granules pass to the heterocysts by this passage. The 

 author regards the heterocyst as a recipient of reserve-substances — an 

 organ for storing up the contents of neighbouring vegetative cells, 

 when these, owing to unfavourable external conditions, or to active 

 spore-formation in the central portion of a filament, become exhausted. 

 In the case of centripetal spore-formation, as in Sphccrozyga, it is possible 

 that the function of the heterocysts may be taken over by the intercalary 

 ones. As regards Brand's observation of the germination of the contents 

 of heterocysts, it stands alone : but Fritsch considers that these bodies 

 may be the remnants of important reproductive organs of the Cyano- 

 phyceae, whose functions have now in great part been taken over by 

 the spores ; and the failure to confirm Brand's observation may lie in 

 the fact that very unusual conditions may be necessary to cause the 

 heterocyst to revert to its former functions, and these extreme conditions 

 but rarely occur. 



Schizomycetes. 



Action of Radium on Micro-organisms.* — A. B. Grim has sub- 

 jected certain micro-organisms to such emanations from radium bromide 

 as passed through thin talc, i.e. the /? and y rays. Experimenting 

 with calf vaccine, he found that the specific germ in no case survived a 

 longer exposure than 22 hours at a distance of 1-2 mm. The ex- 

 traneous micro-organisms of the vaccines employed, viz. S. pyogenes 

 <wreu$, S. pyogenes albus, S. cereus flavus, S. cereus albus, in no case 



* Proc. Roy. Soc., lxxiii. (1904) pp. 375-S1. 



2 r 2 



