184 THE GENESIS OF SPECIES. [CHAP. 



has only recently received a more or less satisfactory 

 solution through the successive concordant efforts of 

 Professor Humphry, 1 Professor Huxley, 2 the author of 

 this work, 3 and Professor Flower. 4 Very few writers, how- 

 ever, have devoted much time or thought to the question 

 of serial homology in general. Mr. Herbert Spencer, in- 

 deed, in his very interesting " First Principles of Biology," 

 has given forth ideas on this subject, which are well 

 worthy of 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 : Animals of a 

 very low grade propagate themselves by spontaneous fission. 

 If certain creatures found benefit from this process of divi- 

 sion remaining incomplete, they would (on the theory of 

 " Natural Selection ") transmit their selected tendency to 

 such incomplete division to their posterity. In this way, 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 imperfectly separated individuals, 

 and be equivalent to a series of separate individuals be- 

 longing to kinds in which the fission was complete. In 

 other words, Mr. Spencer would explain it as the coalescence 

 of organisms of a lower degree of aggregation in one 

 ongitudinal series, through survival of the fittest aggre- 

 gations. This may be so. It is certainly an ingenious 

 speculation, but facts have not yet been brought forward 

 which demonstrate it ; otherwise, this kind of serial homo- 

 logy might be termed " homogenetic." 



1 Treatise on the Human Skeleton, 1858. 



2 Hunterian Lectures for 1864. 



3 Linntean Transactions, vol. xxv. p. 395, 1866. 



4 Hunterian Lectures for 1870, and Journal of Anat. for May 1870. 



