92 THE GERMAN TRANSCENDENTALISTS 



belonging to animals of the most diverse groups. He 

 compares, for instance, the placenta with the gills of fish, of 

 molluscs and of worms, homologising the cotyledons with the 

 separate tufts of gills in Tct/iys, ScylUca and Arenicola (p. 26). 

 This is purely a physiological analogy. He compares the 

 closed anus of the early human embryo with the permanent 

 absence of an anus in Coelentera, and the embryo's lack of 

 teeth with the absence of teeth in many reptiles and fish, in 

 birds, and in many Cetacea (p. 46). 1 These are merely chance 

 resemblances of no morphological importance. He considers 

 bladderworms as animals which have never escaped from 

 their amnion, and Volvo.v as not having developed beyond the 

 level of an egg (p. 7). He lays much stress upon likeness 

 of shape and of relative size, comparing, for instance, the 

 large multilobate liver of the human foetus with the many- 

 lobed liver of lower Vertebrates and of Invertebrates. In 

 general he shows himself, in his comparisons, lacking in 

 morphological insight. 



His treatment of the vascular system affords perhaps the 

 best example of his method (pp. 8-25). The simplest form 

 of heart is the simple tubular organ in insects, and it is under 

 this form that the heart first appears in the developing chick. 

 The bent form of the embryonic heart recalls the heart of 

 spiders; it lies at first free, as in the mollusc Anomia. The 

 heart consists at first of one chamber only, recalling the one- 

 chambered heart of Crustacea. A little later three chambers 

 are developed, the auricle, ventricle, and aortic bulb ; at 

 this stage there is a resemblance to the heart of fish and 

 amphibia. At the end of the fourth day the auricle becomes 

 divided into two, affording a parallel with the adult heart of 

 many reptiles. 



In his large text-book of a somewhat later date, the 

 System f/i-r I'cr^lcicJicuden Anatomic (i., 1821), he works out 

 the idea again and gives to it a much wider theoretic sweep, 

 hinting that the development of the individual is a repetition 

 of the evolutionary history of the race. Meckel was a timid 

 believer in evolution. He thought it quite possible that much 

 of the variety of animal form was due to a process of 



1 Cetacea were generally considered at this lime to be mammals of 

 low organisation. 



