xxxii Obituary Notices of Fellows deceased. 



building up of the perfect form in the pupa is studied in detail, and it is 

 shown that, in insects with a complete metamorphosis, the tissues undergo 

 a breaking down or histolysis into an apparently simple and primitive mass, 

 from which the imago is built up afresh by, as it were, a second embryonic 

 development. Thus the long series of slightly modified progressive steps by 

 which, in the more ancestral groups, the earliest stage is transformed into the 

 latest has been shortened in the more recent forms into a single intermediate 

 stage, in which everything is broken down and built up again from the 

 beginning, establishing the truth of Aristotle's statement that ' the chrysalis 

 has the potentiality of the egg.' 



" Insect development was followed by a great series of memoirs (1874-1880) 

 on the minute Crustacea — Daphnids and Ostracods — and these again by the 

 epoch-making researches into the sexual cells of the Hydrozoa, published in 

 four papers between 1880 and 1882, and, in 1883, in the great quarto 

 monograph, 'Die Entstehung der Sexualzellen bei den Hydromedusen.' 

 With the appearance of this work Weismann's eyesight became too weak 

 for prolonged microscopic research, and he turned to other and more general 

 problems of thought and inquiry. 



" Weismann was attracted early in his career towards the problems of the 

 history and causes of evolution. ' The Origin of Species ' appeared in the year 

 following the publication of his first paper, and in 1868 he brought out 

 ' Ueber die Berechtigung der Darwin'schen Theorie,' followed in 1873 by his 

 paper on the influence of isolation, written in answer to Wagner. The 

 ' Studien zur Descendenz-Theorie ' (1875) included a variety of subjects 

 treated from the evolutionary point of view — the seasonal dimorphism of 

 butterflies, the markings of caterpillars, phyletic parallelism, the transforma- 

 tion of the Mexican axolotl, and the mechanical conception of nature. This 

 important and stimulating work, translated into English, with many additional 

 notes by Eaphael Meldola, and with a preface by Charles Darwin, was pub- 

 lished in 1882. The present writer well remembers the interest with which 

 he looked forward to the parts as they successively appeared and the instant 

 resolution to continue some of the lines of work. 



" The central thought which branched forth so luxuriantly during the last 

 30 years of Weismann's life sprang from his researches on the sexual cells of 

 the Hydrozoa. By these he was led to conclude that, however ordinary their 

 appearance, the germ-cells contain something essential for the species, some- 

 thing which must be carefully preserved and passed on from one generation 

 to another. It was this conclusion, so Weismann told the present writer in 

 1887, which led directly to the hypothesis of ' The Continuity of the Germ- 

 plasm,' with all its far-reaching consequences. In Darwin's pangenesis the 

 germ-cells are derived from the body-cells, whereas in Weismann's contrasted 

 hypothesis the body is an outgrowth from the germ. From this conception 

 Weismann was led to contrast the mortal soma with the potentially immortal 

 germ and to question the hereditary transmission of acquired characters. 

 Excluded from the Darwinian interpretation of germinal variation as a 



