MODERN BIOLOGY 4x1 



By the side of Siebold, Leuckart deserves mention as one of those who 

 contributed towards the progress of biology in the middle of last century. 

 Karl Georg Friedrich Rudolf Leuckart was born in iSiz at Helmstadt, 

 where his father was a business man, and studied at Gottingen, especially 

 under the physiologist Rudolf Wagner; he became a lecturer there, then 

 professor of zoology at Giessen in 1855, and was called thence to the same 

 chair in Leipzig in 1869. There he worked until his death, in 1898. Being 

 still keenly interested in the advancement of science even in his old age, he 

 gathered around him large numbers of pupils up to the end; helpful and 

 warm-hearted, original and good-humoured, he won their affection and was 

 universally praised after his death. 



Leuckart's scientific activities were many-sided and of deep significance. 

 While still a young lecturer he published an epoch-making work, Uber die 

 Morpbologk der wirbellosen Tiere. "Descriptive zoology," he says, "must per- 

 mit of the same comparative, morphological treatment as anatomy." From 

 this point of view he discusses the zoological system prevalent at the time, 

 taking as his starting-point Cuvier, whose type theory he unreservedly de- 

 fends against the earlier belief in one single evolutional series, at the same 

 time upholding the idea of idealistic morphology of a fundamental form 

 after which "nature has constructed" the separate life-forms. Leuckart is 

 definitely opposed to such systematical categories as are based upon nega- 

 tive characters, as, for instance, the Lamarckian group of Invertebrata. Nor 

 indeed do Cuvier' s four types meet the requirements of comparative mor- 

 phology: apart from the Protozoa, whose then still undiscovered structure 

 did not permit of definitive morphological treatment, and the Vertebrata, 

 whose place was already established, Leuckart sets up five fundamental types 

 — namely, Coelenterata, Echinodermata, Vermes, Arthropoda, and Mol- 

 lusca. These have, of course, been generally accepted since then, although 

 with sundry modifications: Vermes have been further divided and Tunicata 

 have been separated from the Mollusca. Through this reform, however, 

 Leuckart brought the system a good step nearer the point that it has reached 

 today. In particular his treatment of the Coelenterata was epoch-making; 

 besides establishing the difference in anatomical structure between them and 

 the similarly radially symmetrical Echinodermata, he explains the curious 

 division of labour that takes place between the individuals in certain colony- 

 building forms within this class, principally in the group Siphonophora, 

 wherein the individuals in a colony are converted for the purpose of per- 

 forming a number of special functions necessary for the welfare of the whole 

 community. As a result of this elucidation of the structure of these so-called 

 "polymorphous" animal stocks, to a certain extent fresh light was thrown 

 on the term "individual" in the animal kingdom. The fact that Leuckart 

 believed he could compare the plants in general with these colony-formations 



