WEISMANN'S DISCOVERY OF IMAGINAL BUDS 643 



and even Lacordaire, in his Introduction a 1'Entomologie published in 

 1834, held on to Swammerdam's theory, declaring that " a caterpillar 

 is not a simple animal, but compound," and he actually goes so far 

 as to say that " a caterpillar, at first scarcely as large as a bit of 

 thread, contains its own teguments threefold and even eightfold in 

 number, besides the case of a chrysalis, and a complete butterfly, 

 all lying one inside the other." This view, however, we find is not 

 original with Lacordaire, but was borrowed from Kirby and Spence 

 without acknowledgment. These authors, in their Introduction to 

 Entomology (1828), combated Herold's views and stoutly maintained 

 the old opinions of Swammerdam. They based their opinions on 

 the fact, then known, that certain parts of the imago occur in the 

 caterpillar. On the other hand, Herold denied that the successive 

 skins of the pupa and imago existed as germs, holding that they are 

 formed successively from the " rete mucosum," which we suppose to 

 be the hypodermis of later authors. In a slight degree the Swam- 

 merdam-Kirby and Speuce doctrine was correct, as the imago does 

 arise from germs, i.e. the imaginal disks of Weismann, while this 

 was not discovered by Herold, though they do at the outset arise 

 from the hypodermis, his rete mucosum. Thus there was a grain of 

 truth in the Swammerdam-Kirby and Spence doctrine, and also a 

 mixture of truth and error in the opinions of Herold. 



The real nature of the internal changes wrought during the 

 process of metamorphosis was first revealed by Weismann in 1864. 

 His discovery of the germs of the imago (imaginal buds) of the 

 Diptera, and his theory of histolysis, or of the complete destruction 

 of the larval organs by a gradual process, was the result of the appli- 

 cation of modern methods of embryology and histology, although 

 his observations were first made on the extremely modified type of the 

 Muscidae or flies, and, at first, he did not extend his view to include 

 all the holometabolous insects. Now, thanks to his successors in 

 this field, Ganin, Dewitz, Kowalevsky, Van Rees, Bugnion, Gonin, 



opment of the imago. But he differs from them in asserting that in this state it is 

 destined to two distinct purposes : first, for the production of the muscles of the 

 butterfly, which he affirms are generated from it in the shape of slender bundles of 

 fibres; and, secondly, for the development and nutrition of the organs formed in the 

 larva, to effect which, he says, it is dissolved again into the mass of blood, and being 

 oxygenated by the air-vessels, becomes fit for nutrition, whence the epiploon appears 

 to be a kind of concrete chyle." (Entwickelungsgeschichte der Schmetterlinge, 

 pp. 12-27.) It seems that Herold was right in deriving the pupa and imago from the 

 hypodermis (his rete mucosum), but wrong in denying that the germs did not preexist 

 in the young caterpillar, and wrong in supposing that the latter originated from the 

 blood, also in supposing that the muscles owe their origin to the fat-body. Swam- 

 merdam, and also Kirby and Spence, were correct in supposing that the imago arose 

 from "germs " in the larva, though wrong in adopting the " emboitement " theory. 



