Life on the Earth, its Origin and Succession. 211 



probable hypothesis, and thus the idea of one general oceanic germ of 

 life, whether we like it or not, must be abandoned. Reasoning of the 

 same kind will convince us that to derive by any probable steps any one 

 great division of the animal kingdom from another, involves too much 

 of a hazardous assumption to be adopted by a prudent inquirer. 



" Take, therefore, the hypothesis in an easier shape, and accept as 

 primary structures in general forms all the great invertebral divisions 

 which reside in water ; let us suppose them capable of indefinite 

 variation, and inquire what is the geological evidence in proof of each 

 later group being derived from some earlier one by descent with modi- 

 fication. Take the least incomplete series of forms, viz. the MoUusca, 

 and undoubtedly the most favourable of all the marine groups for the 

 application of hypothesis. 



" The earliest known Mollusk is the Brachiopod Lingula ; which, as 

 already observed, recurs in all the systems of strata, and is still 

 living. It gives no generic branches. The next earliest are the Dimy- 

 arian genera, Ctenodonta and CucuUella, which cannot be regarded as 

 descended from any conceivable Brachiopod, or accepted as progeni- 

 tors of Modiola, Orthonota, Cardiola or Pleurorhynchus ; still less of 

 their Monomyarian companions, Ambonychia, Avicula and Pterinea, 

 It is inconceivable that from these or anything like them could be 

 derived the Gasteropod, Euomphali, Loxonemae, &c., or that the Heter- 

 opod Bellerophon, the Pteropod Theca, or the Cephalopod Orthoceras, 

 are consanguineous, any one of them with any other. All these grea 

 classes then are according to the evidence equally aboriginal, though no 

 of equal antiquity. 



" Without bringing in similar results from the other invertebral 

 classes we may boldly affirm that the later series of Cambro-Siluriau 

 life cannot possibly be derived from the earlier series, according to the 

 evidence preserved to us ; but on the contrary requires absolutely the 

 admission of separate stemmata, certainly for every principal group, 

 apparently and probably so for every genus or natural assemblage of 

 much resembling forms with similar structures. 



" The explanation offered by most palaeontologists is that these several 

 stemmata are of independent origin, separate creations in fact, using 

 this term to indicate a process unknown to us, by which the Creator has 

 provided for the appearance of new forms and structures at definite 

 times and in certain places, which it is in the province of palaeontology 

 to search out. The explanation offered in the hypothesis of Mr. Darwin, 

 is that the groups of life which appear to be and really are distinct, in 

 the Cambro-Silurian rocks, are not aboriginal forms ; but derived from 

 progenitors of far earlier date, belonging to few types or to one ; the 

 original form, and the transition forms being unknown to us. 



" Now they are not unknown to us by any impossibility of being 

 preserved, for the strata of the Carabro-Silurian series are of a kind in 

 which organic remains of great delicacy are often preserved, and indeed 

 such are preserved in these very strata ; and by the hypothesis the life- 

 Structures which are lost must have only gradually differed in their 



