THE MORPHOLOGICAL COMPOSITION OP ANIMALS. 99 



sometimes even like pairs of eyes, also have like internal 

 organs. Each has its enlargement of the alimentary canal; 

 each its contractile dilatation of the great blood-vessel; each 

 its portion of the double nervous cord, with ganglia when 



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these exist ; each its branches from the nervous and vascular 

 trunks answering to those of its neighbours; each its simi- 

 larly answering set of muscles; each its pair of openings 

 through the body-wall; and so on throughout, even to the 

 organs of reproduction. That is to say, every segment is in 

 great measure a physiological whole — every segment con- 

 tains most of the organs essential to individual life and mul- 

 tiplication: such essential organs as it does not contain, 

 being those which its position as one in the midst of a chain, 

 prevents it from having or needing. If we 



ask what is the meaning of these homologies, no adequate 

 answer is supplied by any current hypothesis. That this 

 " vegetative repetition " is carried out to fulfil a prede- 

 termined plan, was shown to be quite an untenable notion 

 (§§ 133, 134). On the one hand, we found nothing satis- 

 factory in the conception of a Creator who prescribed to him- 

 self a certain unit of composition for all creatures of a par- 

 ticular class, and then displayed his ingenuity in building up 

 a great variety of forms without departing from the " arche- 

 typal idea." On the other hand, examination made it mani- 

 fest that even were such a conception worthy of being enter- 

 tained, it would have to be relinquished; since in each class 

 there are numerous deviations from the supposed " archetypal 

 idea." Still less can these traits of structure be accounted 



