darwin and after darwin. 67 



Series 3. — Fumari^e officinales. 

 F. officinalis L. 

 F. Vaillantii Lois. 

 F. 'parvijiora Lamk. 

 F. micrantha Lag. (F. densijiora DC. p.p.?). 77 f "R 



Darwin and after Darwin. By the late Gr. J. Romanes. Part iii. 

 Post-Darwinian Questions. Isolation and Physiological Se- 

 lection. 8vo, pp. viii, 181. London: Longmans, Green & Co. 

 1897. 

 Three only of the six chapters of this, the concluding volume 

 of Mr. Romanes' last work, were in type at the time of his death. 

 These, the first two and the last, deal with Isolation. For the 

 selection and arrangement of the other three chapters the editor, 

 Prof. Lloyd Morgan, is responsible. Their subject is physiological 

 selection — in the opinion of the author a very important form of 

 isolation. There are also three appendices ; the first embodies 

 Mr. Gulick's criticism of Mr. Wallace's views on physiological 

 selection ; the second is entitled an examination by Mr. Fletcher 

 Moulton of Mr. AVallace's calculation touching the possibility of 

 physiological selection ever acting alone ; the third is made up of 

 some extracts from the author's note-books, and deals mainly 

 with physiological selection and cross-infertility. The first two are 

 inserted in accordance with the author's expressed injunctions. 

 A portrait of the Rev. J. Gulick forms the frontispiece to the 

 volume — a fitting compliment to a naturalist of whom the author 

 says at the opening of the first chapter: "To his essays on the 

 subject [of Isolation] I attribute a higher value than to any other 

 work in the field of Darwinian thought since the date of Darwin's 

 death." "Indeed I believe with Mr. Gulick that in the principle 

 of Isolation we have a principle so fundamental and so universal, 

 that even the great principle of Natural Selection lies less deep, 

 and pervades a region of smaller extent." Along with Heredity 

 and Variation, Isolation forms the tripod on which is reared the 

 whole superstructure of organic evolution. 



Isolation is defined as the prevention of intercrossing between a 

 separated section of a species or kind and the rest of that species or 

 kind. Such separation may be due to geographical barriers, to 

 migration, or to any other circumstances leading to exclusive 

 breeding within the separated group. It is a genus with two 

 species, Apogamy and Homof/aint/. These were, Romanes thought, 

 new words coined by himself to describe indiscriminate and dis- 

 criminate isolation respectively. They are, however, well known 

 to botanists under quite a different meaning. The difterence 

 between indiscriminate and discriminate isolation was pointed out 

 by Mr. Gulick, who used the terms separate and segregate breeding 

 to express the two forms. Indiscriminate isolation occurs, for 

 instance, when a shepherd divides a flock of sheep without regard 

 to their characters; but if he places all the white sheep in one field, 

 and all the black sheep in another field, he is isolating one section 

 from the other discriminately. 



