184 THE GENESIS OF SPECIES. [CiiAr. 



has ouly recently received a more or less satisfactory 

 solution throuLili the successive concordant efforts of 

 I'rofessor Huni])liry,i Professor Huxley,- the author of 

 this work,^ and Professor Flower.* 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 ^\•ell 

 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 

 " Xatural Selection ") transmit their selected tendency to 

 such incomplete division to their posterity. In this way, it 

 is conceivable that animals mifilit arise in tlie form of lonij- 

 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, ^Ir. Spencer would explain it as the coalescence 

 of organisms of a lower decjree of acj^rejiiation 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." 



^ Trcatiso on the Huni.in Skel'iton, 1S58. 



-' Huuteiian Lectures for 1864. 



^ Liiniipan Transactions, vol. xxv. \\. 39r», 1866. 



■• Huntcrian Lectures for 1S70, and Journal of Anat. for May 1870. 



