272 



The remaining portion of the book consists of three chapters 

 devoted respectively to the sexual phenomena, the special 

 morphology of the nucleus, and some physiological problems 

 of the Protozoa. In the first of these the phenomena of 

 conjugation are considered under four heads, which may represent 

 stages in the evolution of sexual reproduction. There is the 

 union, first of exactly similar adult cells, then of individuals 

 only differing somewhat in size, thirdly of reduced individuals 

 (swarm spores), and lastly of specialised individuals (spermato- 

 zoa and eggs). The chapter on the morphology of the nucleus 

 is a very valuable one, as it contains an extremely good account 

 of the facts brought to light by the foremost recent investi- 

 gators. The general conclusion is that the nucleus itself and 

 also the mitotic figures in the Protozoa are much less 

 complex than in the higher animals and plants. The physio- 

 logical problems dealt with in the last chapter are intra-cellular 

 digestion, respiration, secretion and excretion, and irritability, 

 the last named leading to an interesting discussion of the 

 question as to the real nature of the apparently conscious 

 activities of the Protozoa. 



Appended to each chapter are short bibliographies on the 

 subjects dealt with, and at the end of the volume there is 

 a long list of books and papers, to" most of which reference 

 has been made in the text. There is a double index : the 

 first of authors, with an indication of the subjects mentioned 

 in connection with their names, and the second of subjects. 

 The illustrations are exceptionally good for a text-book, a 

 large number of them being original, and most of the others 

 being copies from recent papers. 



Apart from its value as a storehouse of facts, the book 

 will, we believe, have a stimulating effect in the direction of 

 encouraging original research. The limits of our present 

 knowledge in numerous cases are so clearly brought out that 

 the student can scarcely fail to see the many possible openings 

 for investigation. To take a single instance (p. 127), it 

 seems that, in the Choanofiagellata (collared monads), it is 

 by no means certain whether the mouth is within the collar 

 (as maintained by Saville Kent and others), or not. Here, 

 then, is a piece of work which certainly ought to be taken 

 in hand at once. The beautiful, though excessively minute, 



