INTRODUCTION. 



out the grain from the chaff (though his critical spirit found 

 some relief in the latter task), but also caused him much labour, 

 inasmuch as at almost every turn new problems suggested them- 

 selves, and demanded inquiry before he could bring his mind 

 to writing about them. This desire to see his way straight 

 before him, pursued him from page to page, and while it has 

 resulted in giving the book an almost priceless value, made 

 the writing of it a work of vast .labour. Many of the ideas 

 thus originated served as the bases of inquiries worked out by 

 himself or his pupils, and published in the form of separate 

 papers, but still more perhaps never appeared either in the 

 book or elsewhere and were carried with him undeveloped and 

 unrecorded to the grave. 



The preparation of this work occupied the best part of his 

 time for the next three years, the first volume appearing in 

 1880, the second in 1881. 



In the autumn of 1880, he attended the Meeting at Swansea 

 of the British Association for the Advancement of Science, 

 having been appointed Vice-President of the Biological Sec- 

 tion with charge of the Department of Anatomy and Physio- 

 logy. At the Meetings of the Association, especially of late 

 years, much, perhaps too much, is expected in the direction 

 of explaining the new results of science in a manner inter- 

 esting to the unlearned. Popular expositions were never 

 very congenial to Balfour, his mind was too much occupied 

 with the anxiety of problems yet to be solved ; he was there- 

 fore not wholly at his ease, in his position on this occasion. 

 Yet his introductory address, though not of a nature to interest 

 a large mixed audience, was a luminous, brief exposition of 

 the modern development and aims of embryological investi- 

 gation. 



During these years of travail with the Comparative Em- 

 bryology the amount of work which he got through was a 

 marvel to his friends, for besides his lectures, and the re- 

 searches, and the writing of the book, new labours were de- 

 manded of him by the University for which he was already 

 doing so much. Men at Cambridge, and indeed elsewhere as 

 well, soon began to find out that the same clear insight which 

 was solving biological problems could be used to settle knotty 



