520 



question of sex and the sexual process, and as any theory- 

 relating to the origin of sex in the higher animals and plants 

 must be founded on a knowledge of the origin and signification of 

 the syngamic process in the Protista i.e. organisms belonging to 

 what has been style d by the author the " cellular grade " the 

 importance of this section is readily seen. 



Any attempt at a " natural " classification of the Protozoa 

 must be fraught with many difiiculties, for before deciding on the 

 afiinities of any organism it is necessary to know its life- history,, 

 and in many cases that is unknown, or but imperfectly known. 

 In the Systematic Review of the Protozoa the avithor adopts 

 the four old-established divisions or classes : Sarcodina, Mas- 

 tigophora, Sporozoa and Infusoria. The afiinities of the para- 

 sitic forms are discussed, and these are of very great interest 

 from a biological point of view. In the Metazoa parasitism 

 seems to simplify the life-cycle, while in the Haemofiagellates,. 

 or blood-parasites, and in the intra-corpuscular Haemosporidia, 

 of which the malarial parasite is an example, the life-cycle has 

 increased in complexity, especially as regards sexual reproduc- 

 tion. This has probably arisen as a result of the life-cycle 

 being partly spent in an intermediate invertebrate host. The 

 opinion that the Haemofiagellates have arisen along two distinct 

 lines of ancestry is accepted, but accepted with a caution. 



The majority of the figures have been specially drawn from 

 the original sources or from actual preparations, and the artists 

 are to be congratulated on their share in the work. 



The bibliography is grouped under the chapter headings, and 

 includes over eight hundred titles ; this, with an index, com- 

 pletes a work for which the author deserves the highest praise. 



