368 THE HISTORY OF BIOLOGY 



which has been so widely studied in modern times and which, not long be- 

 fore Rathke's period, had been thought to be a worm of a mollusc. Rathke's 

 monograph was the first detailed anatomical description of the animal and 

 was written with the same thoroughness that characterized his embryologi- 

 cal investigations. His abundant and valuable writings further contain several 

 monographs on crustaceans, both independent and parasitic, molluscs and 

 worms, as also a number of monographs on the vertebrates — for example, 

 on the lemming — which are worthy of mention as examples of Rathke's 

 extensive and radical research-work. 



The third in order of the above-mentioned pioneers of embryology was 

 Heinrich Christian Pander (1794-1865). Born at Riga, the son of a wealthy 

 banker, he was able to give undivided attention to scientific work, which 

 had attracted him from an early age. He studied at Dorpat, Berlin, and Got- 

 tingen and afterwards, having made the acquaintance of von Baer, at Wiirz- 

 burg in the latter's company. There he carried out his pioneer work on the 

 development of the embryo of the chick, the results of which, thanks to 

 his great wealth, he was able to publish in a very fine edition. In 182.6 he 

 became an academician at St. Petersburg, but the very next year he resigned 

 and lived for some time as a landowner in the neighbourhood of Riga. In 

 1842. he entered the Russian Mining Board, after which he published only 

 works on geology. 



Discovery of the germinal layers of the hen s embryo 

 Pander's above-mentioned treatises on the development of the hen's &gg, 

 which were published as early as 1817, were the fruits of work carried out 

 under the guidance of Dollinger and with the collaboration of von Baer. 

 They thus represent to a certain extent the basis on which the latter scien- 

 tist worked further, although there is no doubt that while they were being 

 written, the younger of the two friends came under the influence of the elder. 

 As Pander's greatest service should be recorded the fact that, taking as his 

 starting-point the preliminary work of Malpighi and C. F. Wolff, he dis- 

 tinguishes the different layers out of which the organs of the chicken embryo 

 are built up. These layers, which, following Wolff, he names '^Blatter'' — a 

 relic of the latter's attempts to compare plants and animals anatomically — 

 were afterwards further investigated by von Baer and have since then formed 

 the foundations of modern embryology. In his presentation of the continued 

 course of development of the embryo, however, Pander is not to be compared 

 with his above-mentioned contemporaries and he was unable to follow up 

 the promising ideas that he had produced in his early work. A work Ver- 

 gleichende Osteologie, which he published as an edition de luxe in collaboration 

 with the artist d' Alton during his visit to Germany, and which attracted 

 the attention of Goethe, has not the same interest as his embryological 

 works, and upon his return home he divided his genius between a number 



