viir.] iioMcn^oGiES. 177 



sent the most obvious and strikinfr- serial homology — 

 almost the only serial homolog-y noticeable externally. 



The facts of serial homology seem hardly to have excited 

 the amount of interest they certainly merit. 



Very many writers, indeed, have occupied themselves 

 with investigations and speculations as to what portions 

 of the leg and foot answer to what ])arts of the arm and 

 hand, <a question which has only recently received a more 

 or less satisfactory solution through the successive con- 

 cordant elTorts of Prof. Humphry,^ Prof. Huxley,* the 

 author of this work,* and Prof. Flower.' Very few writers, 

 however, have devoted much time or thought to the 

 (piestion of serial homology in general. Mr. Herbert 

 Spencer, indeed, in his very interesting "First Principles 

 of J5iology," has given forth ideas on this subject which 

 are well worthy careful perusal and consideration, and 

 some of which apply also to the other kinds of homology 

 mentioned above. He would explain the serial homologies 

 of such creatures as the lobster and centipede thus: Ani- 

 mals of a very low grade propagate themselves by sponta- 

 neous fission. If certain creatures found benefit from this 

 process of division remaining incomplete, such creatures 

 (on the theory of " Natural Selection " ) would transmit 

 their selected tendency to such incomplete division to their 

 posterity. In this Avay, it is conceivable that animals 

 might arise in the form of long chains of similar segments, 

 each of which chains would consist of a number of imper- 

 fectly separated individuals, and be equivalent to a series 

 of separate individuals belonging to kinds in which the 

 fission was complete. In other words, Mr. Spencer would 

 ex])lain it as the coalescence of organisms of a lower 



' Treatise on the Human Skeleton, 1858. 



^•Iluntorian Locturoa for 18G4. 



' liinnfcan Traupactions, vol. xxv. p. .TOR, IRfifi. 



• Iluntcrian Lectures for 1870, and Journal of Anat. for May, IS^O. 



