70 SUMMARY OF CURRENT RESEARCHES RELATING TO 



and as a result, the particle becomes a centre of carbonic acid secreted 

 by the resting animals. Carbonic acid exerts a strongly attractive 

 influence on organisms in general ; and these, during the course of their 

 random wanderings, are likely to come within the acidulated area, and 

 are then retained there by the negative reaction of the surrounding 

 water. The same phenomenon explains the swarming of individuals 

 round a solid particle which is already covered by others, There is 

 thus no action at a distance, the swarming is an accidental result of the 

 active movements of the unstimulated animal. Quite similarly there is 

 no directly attractive agent, the swarming in any particular area being 

 due to the repellent effect of the surrounding area. The mechanism 

 of repulsion is, that contact with the repellent substance causes the animal 

 to reverse its cilia, move backwards, make a half turn, and then move 

 forwards again. Under ordinary circumstances the result is to cause 

 the animal to move away from the repellent substance ; but the absence 

 of any " intelligence " in the process is shown by the repetition of the 

 same movements when the Paramsecia are placed in water impregnated 

 throughout with the noxious reagent. The result is that, strictly 

 speaking, it is as untrue to say that Paramsecium is repelled by any 

 agent or condition as it is to say that it is attracted. It is rather true 

 that certain agents produce a reaction which is not directly related to 

 the position of the source of stimulus, but which is determined by the 

 structure of the organism. 



Conjugation in Infusoria.* — S. Prowazek has studied the structure 

 and life-history of Bursaria truncatella (O. F. M.) Clap, et L. The 

 macronucleus is a long ribbon-shaped structure tapering towards the 

 ends. It possesses an alveolar structure with a central denser band. The 

 micronuclei are numerous and are not always easy to see. Conjugation 

 follows a period of rapid division, and is heralded by restless swimming 

 movements. In the first period the most marked alteration is seen in 

 the macronucleus, which increases in length and becomes coiled. Later 

 it takes on a rosary-like form, and ultimately breaks up into some 6-12 

 segments, each containing one or more rounded masses of chromatin. 

 These undergo degeneration later. Meanwhile the micronuclei increase 

 in size and divide by means of spindles. One of the nuclei produced 

 forms the fertilisation-spindle, the others are to be regarded as analogous 

 to reducing divisions. The fertilisation-spindle divides into a stationary 

 and a wandering nucleus. After the fusion the new nucleus divides up 

 to form the numerous micronuclei of the normal organism. These 

 micronuclei separate from one another, and ultimately a varying number 

 of them fuse together to form the new macronucleus. 



The author has also studied the structure] and life-history of 

 Stylonychia pustulata, and gives a detailed account of his observations, 

 with some notes on habits. 



New Myxosporidium.f — Mr. Hagenmuller describes Nosema stephani 

 sp. n. (genus Glugea Thelohan) from Flesus passer Moreau. This is 

 interesting, since '1 helohan regarded Pleuronectid fishes as refractory to 

 myxosporidial infection, though the conditions of their life seem such 



* Arbeit. Zool. Inst. Univ. Wien, xt (1899) pp. 195-268 (4 pis. and 4 figs.). 

 t Collates Rendus, cxxix. (1899) pp. 836-9. 



