754 TRANSACTIONS OF SECTION K. 



presence. By appropriate treatment 1, 2, and 4 can all be rendered motile, hence 

 all the Coccacese are motile. 



The next division — Bacteriaceae — is divided as follows : — 



1. Bacterium . . Non-motile. 



2. Bacillus . . . Motile, cilia all round. 



3. Pseudomonas . . Motile, cilia polar. 



By the same treatment the forms classified as Bacterium can be made motile, 

 so that the whole of this group has motile forms, and the distinction between 

 Bacterium and Bacillus is non-existent. 



The third division — Spirillacese —is divided as follows : — 



1. Spirosoma . . No organs of motion. 



2. Microspira . . 2-.S polar cilia. 



3. Spirillum . . . 5-20 polar cilia. 



4. Spirochfete . . Cells without organs of motion, but 



possessing a wavy motion. 



Spirillum has often a larger number of cilia than twenty. On the result of the 

 above investigations there can be little doubt that the genera Spirosoma and 

 Microspira will have to be merged into the genus Spirillum. 



We can therefore affirm that motility, either potential or actual, is a 

 characteristic of all the forms of the three divisions — Coccaceae, Bacteriaceae, and 

 Spirillacese. 



MONDAY, AUGUST 6. 

 Joint Discussion ivith Section D on Fertilisation. 



The following Papers were read : — 



1. The Nature of Fertilisation. By Vernon H. Blackman. 



An attempt is here made to give a brief account of some of the recent work ou 

 which the more modern views of the nature of fertilisation are based. The term 

 fertilisation is used in its widest sense, to include any gametic union of cells and 

 nuclei, and is thus equivalent to the syngamy of Hartog. 



In the cytological life-history of the higher organisms which reproduce them- 

 selves sexually three main cytological stages are to be observed— a stage of cell 

 and nuclear union, a stage of somatic divisions, and a stage of reduction which 

 halves the number of chromosomes. The advantages of gametic union have 

 been supposed to be rejuvenescence and the union of two lines of descent. The 

 rejuvenescence theory is supported by the observations of Maupas and of Calkins 

 on Protozoa, but both views are difficult to apply generally, in view of the groups 

 which show no gametic unions, and the large number of organisms, especially plants, 

 in which the fusing cells or nuclei are very closely related. 



In view of the general constancy in the number of chromosomes, reduction is a 

 necessary corollary to fertilisation ; and since Van Beneden in 1883 showed that in 

 Ascaris the number of chi-omosomes in the sexual cells was only half the number 

 normal for the somatic cells, various theories have been put forward as 

 to the method by whicli reduction is brought about. The reduction has been 

 shown to take place at a definite point in the life-cycle (at least 

 in the higher animals and plants), to be associated with a peculiar con- 

 densation of the chromatin of the nucleus (synapsis), and with a tetrad 

 division of the mother-cells concerned. The general theory of the indivi- 

 duality, or, rather, autonomy, of the chromosomes has gained ground, and atten- 

 tion has been focussed on the question of the n.ature of the reduction process in 

 connection with the rediscovery of Mendeliau inheritance. The most iuiportant 



