MODERN SCIENCE. 147 



animals, and a determination of their mutual relations and 

 lines of descent. His "Anthropogenic" is an elaboration of 

 the same principles to the special problem of the evolution of 

 man. It includes subjects which have been exercising 

 biologists' minds of late years such as the Gastraea theory, 

 the Ccelum theory, and the nature and origin of segmentation 

 into which our limits do not allow us to enter. He 

 vigorously defends what he calls the " fundamental law of 

 biogenesis/' known in England as the recapitulation theory, 

 according to which the actual development of an animal is a 

 repetition of the ancestral development of the species ; or, 

 as it has been put, animals in their development climb up to 

 their own genealogical trees a theory generally accepted by 

 biologists. (See Von Baer.) He was amongst the first who 

 realised and taught that doctrine. He strongly dissents from 

 Weismann's teaching with regard to heredity pointing out 

 that the existence of germ-plasm is as yet a mere conjecture, 

 and maintaining that acquired characters are transmitted. He 

 holds that the ancestors of the Vertebrates must be looked for 

 amongst the segmented Turbellarian worms. The weak 

 points of Haeckel's teaching lies in human embryology, " the 

 difficulties of the problem of which he lays aside " a great 

 deal, mainly due to the labours of the celebrated Leipzig 

 Prof. His amongst others, and known for certain, he entirely 

 ignores. Haeckel's works contain genealogical tables, one of 

 his usual modes of exposition, which, strongly suggestive as 

 they are, are not always accepted by naturalists. Yet, his 

 zoological classification is on the whole considered as one of 

 the most perfect ever devised. Haeckel, it should also be 

 remembered, has made sponges a particular study, and is held 

 as one of the few authorities on that special branch of 

 organisms which yields strong evidence of evolution. 



Haeckel was not alone in Germany in working out the 

 problems of life initiated by Darwin. To speak of a few 

 only, the two Mullers (Fritz and Hermann) till the same 

 field with earnest conviction and intelligence : the first 

 collected his fine " Facts for Darwin/' which abound in 

 instances and evidences of organic development ; the second 

 observed with German patience and thoroughness the action 



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