(574 ZOOLOGY sect. 



while under the head of Vermes are inchided all the phyla re- 

 cognised at the present day, except Chordata and Arthropoda. 



Other naturalists of the eighteenth century must be briefly 

 referred to. Bonnet introduced the idea of a " scale of beings " 

 (dchelle des Stres), conceiving the true classification to be a linear 

 one, passing in a single series from the lowest to the highest 

 forms. This conception was opposed by Pallas, who introduced 

 the true conception of representing the relationships of the 

 various groups under the form of a much-branched tree. Spal- 

 lanzani made numerous investigations on reproduction, and, 

 together with Bonnet, Bufifon, and Haller, strongly supported the 

 doctrine of pre-formation already referred to. Haller summed 

 up the position by stating emphatically that there was no such 

 thing as development or differentiation, no part of the body being 

 made before another, but all parts simultaneously created. It 

 followed, as a natural corollary from this view, that the germ 

 destined to give rise to an animal — i.e., the ovum according to 

 the ovulists, the sperm according to the spermatists— contained 

 within itself the germ of the ne.xt generation, that of the next, 

 and so on, ad infinitum, so that the first created male or female 

 of each species contained within its sperms or ova the germs of 

 all future generations, enclosed one within the other, like a nest 

 of Chinese boxes. Bufifon, as the result of numerous experiments, 

 came to the conclusion that the ovary secretes a seminal fluid 

 containing moving particles analogous to sperms, and, from this 

 erroneous observation, framed a theory which is an interesting 

 anticipation of Darwin's Pangenesis (p. 663) — namely, that organic 

 particles, derived from all parts of the body, occur in the seminal 

 fluids of the two sexes, and that the union of these in the uterus 

 " determines them to arrange themselves as they were in the 

 individuals which furnished them." 



The theory of pre-formation (as then understood) was practically 

 demolished, and that of epigenesis, or new formation, established 

 on a firm basis, by Caspar Friedreich WolflF, who, at the age 

 of twenty-six — in 1759 — gave the most accurate account of the 

 development of the Chick hitherto known, and showed clearly 

 that there was no pre-formation of the various parts, but a 

 gradual differentiation from a layer of organised particles, or, as 

 we should now say, from a cellular blastoderm. 



Another great eighteenth century name is that of John Hunter, 

 the most profound comparative anatomist and physiologi.st of his 

 time. He was not a zoologist in the narrow sense of classifier, 

 but his exquisite investigations on the various systems of organs 

 and their functions throughout the animal kingdom furnished the 

 science with a foundation of wide and exact knowledofc which was 

 of far more importance than the most cunningly devised system of 

 classification. Important anatomical investigations were also 



