3 66 THE HISTORY OF BIOLOGY 



had adopted from contemporary natural philosophers, as for instance Oken's 

 theory of the head's being composed of vertebrae and of the jaws' having the 

 qualities of ribs. Others again he has certainly invented himself — for ex- 

 ample, the theory that the vertebrate animals are composed of a number of 

 tubes lying inside one another in the shape of the figure 8. He reaches the 

 extreme heights of Schellingism with a scheme he works out, according to 

 which the three tubes lying within one another are each divided into a 

 positive and a negative half; the epidermis, the muscles, and the nervous 

 membrane are thus given a plus sign, while the cutis, the bones, and the 

 nerve-fibres are denoted by a minus sign. Strangely enough, one comes across 

 fancies of this kind in many of the eminent biologists of that period; some 

 have already been mentioned, others will be discussed later on. It would be 

 quite irrational, however, to accept these confessions of the weakness of 

 the period for more than what they are; they are certainly striking from the 

 point of view of cultural history, but their significance, whether for the 

 activities of the scientists named or for their contribution to the general 

 development of science, should at any rate not be exaggerated. 



Martin Heinrich Rathke may claim an eminent place by the side of 

 von Baer among the pioneers of embryology. He was born in 1793 at Danzig 

 of a wealthy burgher family. He studied at Gottingen under Blumenbach, 

 practised for a time as a doctor in his native town, was invited to Dorpat 

 in 18x9 as professor in physiology and thence, as von Baer's successor, to 

 Konigsberg, where he worked until his death, in i860. Being personally 

 a lovable character, keenly active on behalf of his science, constantly seeking 

 to increase his knowledge by research work at home and abroad, he was 

 universally esteemed by his colleagues and pupils. 



Rathke's work as a biologist was many-sided and important. Among 

 his earliest works was an article published in a journal, "On the Develop- 

 ment of the Respiratory Organs in Birds and Mammals," which in point of 

 value may be compared with von Baer's above-mentioned embryological 

 treatises. It has already been pointed out that Rathke discovered the gill- 

 slits in the embryo of birds and mammals, as well as the ramification of 

 blood-vessels connected therewith. He further compared them with those of 

 the fishes and followed their later development — how the gill-slits dis- 

 appear and how the blood-vessels adapt themselves to the lungs, which are 

 developed from an expansion of the front part of the digestive canal. He has 

 also described and compared the development of the air-sacs of birds and the 

 larynx of birds and mammals. In another work he gives an account of the so- 

 called Wolffian bodies discovered by him, which he characterizes as "head 

 kidneys" (pronephros), and which for a time performed the function of excre- 

 tal organs, only to disappear later according as the true kidneys developed, 

 while their efferent ducts in certain animals serve as part of the sexual organs. 



