132 On the Genetics of the Ciliate Protozoa 



or implicitly) on these : I have then reviewed and commented upon the 

 work which has been done since his day : and finally I have drawn a few 

 of the more obvious conclusions — conclusions which will appear to many, 

 I am afraid, the least satisfactory feature of this article. Siiife the works 

 of many of the older investigators — Blitschli, Balbiaiii, I'^iigelmann, and 

 the rest — are in many ways no less admirable and important than the 

 more modern researches of R. Hertwig, Enriques, Jennings, Popofif, 

 Woodruff, and others, I have more than once referred to these; but 

 such references have been relegated to footnotes. 



To facilitate the numerous cross-references in the body (if the papei- 

 I have adoj)ted the plan of numbering the paragi-aphs. A parenthetic 

 reference thus (§ x) signifies that on refeniug to the paragraph 

 numbered x, the reader will find additional information relating to 

 the matter under discussion. 



I am fully conscious of having made many omissions, but I trust 

 that uiisstatements concerning the facts are few. Such criticisms as 

 I have ventured to make are based upon my personal knowledge of the 

 ciliates, and I should be the first to welcome corrections or counter- 

 criticisms. 



A general analysis of the subject-matter of this article will be found 

 on page 183. I have added it to facilitate reference to the subjects dealt 

 with : and I have placed it at the end because I should prefer the article 

 to be read as a whole before special sections of it are consulted. My 

 commentary aims at being a consistent whole, and its several parts — 

 considered singly — may therefore appear obscure or incomprehensible. 

 If the reader's curiosity has been sufficiently excited, he will accordingly 

 proceed now to the first chapter. 



CHAPTER I. 



Tlie Organization of a Ciliate, and the Chief Events in its Life. 



1. A typical ciliate possesses a peculiar organization, which is often 

 misunderstood. Its body is built upon the plan shown in Fig. 1 (A). 

 It is clothed, more or less, with locomotory ciliary appendages (c) often 

 greatly differentiated. The animal possesses a mouth {mo.) defining 

 the ventral surface ; and as one end is specialized as a " head " end, we 

 can further distinguish anterior and posterior, dorsal, and right and left 

 lateral regions of the body — which is generally asynnnetric. In the 

 protoplasm there are usually vacuoles (/('.) in which food is digested. 



