118 Transactions of the Royal Microscopical Societi/. 



it very probable that molecularly combined water really plays a part 

 in their structure ; and on the whole we may, I think, base our 

 provisional calculations on the total number of molecules given 

 above. 



The Theory of Invisible Germs. 



The relation between the size of the smallest object that can be 

 seen, and that of the ultimate molecules of living matter, is mani- 

 festly a question of great importance in connection with the theory 

 of germs. If the ultimate molecules were much larger than they 

 appear to be, there would be serious objections to the theory ; but, 

 as far as_ we can judge, they are sufficiently small to make it possible 

 for an almost endless variety of germs to exist, each having a dis- 

 tinct structural character, and yet each so small that there is no 

 probability of our ever being able to see them, even as indefinite 

 points. Thus, according to the principles described above, a sphere 

 of organized matter one-tenth of the diameter of the smallest particle 

 that could be clearly defined with our highest powers, might con- 

 tain a million molecules of albumen and molecularly combined 

 water. Variations in number, chemical character, and arrange- 

 ment, would in such a case admit of an almost boundless variety 

 of structural characters. The final velocity with which such ex- 

 tremely minute particles would subside in air must be so slow that 

 they could penetrate into almost every place to which the atmo- 

 sphere has access. 



Darwin's Theory of Pangenesis. 



Darwin's theory of pangenesis is an attempt to give something 

 like a reasonable explanation of the phenomena of inheritance, and is 

 not necessarily connected with the question of the evolution of new 

 species. A full account of the theory will be found in his work on 

 the variation of animals. At p. 374 of vol. ii. he says that "he 

 assumes that cells before their conversion into completely passive or 

 formed material, throw off minute granules or atoms, which circulate 

 freely throughout the system, and when supplied with proper nutri- 

 ment multiply by self-division, subsequently becoming developed 

 into cells like those from which they were derived. These granules 

 for the sake of distinctness may be called cell-gemmules, or, as the 

 cellular theory is not fully estal3lished, simply gemmules. They are 

 supposed to be transmitted from the parents to their offspring, and 

 are generally developed in the generation which immediately suc- 

 ceeds, but are often transmitted in a dormant state during many 

 generations, and are then developed. Their development is sup- 

 posed to depend on their union with other partially developed cells 

 or gemmules which precede them in the regular course of growth. 



