NOTES. 477 



100 (i. 361). The agreement among the germ-forms of 

 various Mammals is instructive especially because it shows us 

 how, by diversity in the mode of evolution, the most diverse 

 structures can originate from one and the same form. As we 

 actually see this in germ-forms, we may hypothetically assume 

 the same to have occurred among tribe-forms. Moreover, 

 this agreement is never absolute identity, but always only 

 the very greatest similarity. Even the germs of the various 

 individuals of a species are never actually identical. 



101 (i. 366). The law of the ontogenetic connection of 

 systematically allied animal-forms has many apparent exceptions. 

 These are, however, fully explained by the adaptation of the 

 germ to kenogenetic conditions of existence. Where the palin- 

 genetic form of evolution of the germ has been accurately 

 transmitted by heredity, that law is always in force. Cf. Fritz 

 Miiller, " Fur Darwin " (note 111). 



102 (i. 367). Earliest human germs. Cf. Kolliker, " History 

 of the Evolution of Man " (" Entwickelungsgeschichte des Men. 

 schen." 2nd edition, 1876, pp. 303-319). Also Ecker, "Icones 

 physiologic^." Leipzig, 1859. Plates XXV.-XXXI. The 

 earliest human germs which have yet been certainly recognized, 

 were from twelve to fourteen days old, and were observed by 

 Prof. Allen Thomson, of Glasgow. No opportunity has ever 

 occurred for the observation of earlier germs. 



103 (i. 369). Human germs of three weeks (twenty to twenty- 

 one days) exhibit in their whole structure that phylogenetic stage 

 of evolution which, among extant Vertebrates, is represented by 

 the Cyclostomi (Lampreys and Hags, vol. ii. p. 103), and which 

 must be referable to extinct Monorhine ancestors of similar 

 structure. 



104 (i. 370). Human germs of four weeks (twenty-five to 

 thirty days), on the whole, exhibit in their whole structure that 

 phylogenetic stage of evolution, which is exhibited in Sharks 

 and Rays, among extant Vertebrates, and which is referable to 

 similar extinct Primitive Fish ancestors (Proselachii). Of course 

 this comparison is affected by various kenogenetic modifications 



