THE CHAIN OF SFECIES. 571 



same rule, some geophilidce, mentioned by Dr. Carpenter, must reach 

 to three hundred and twenty — each segment, remember, having a 

 2'w«s^-separate organization, separate circulation, separate nerves, and 

 separate appendages for aeration and locomotion. Their close and 

 intimate connection does not prevent easy analysis into distinct sys- 

 tems for each segment. 



Again, however, Nature soon discovers her mistake. The highest 

 concentration of energy cannot be reached in this way, and she makes 

 trial of a new plaa. She seeks to modify and expand the elements, 

 and to bring them into closer contiguity. Gathering up her forces 

 into a few central segments, the rest are lopped off. This is actually 

 the history seen in some embryones. In insects, finally, the highest of 

 the segmentarians, there are only about twenty well-pronounced seg- 

 ments. Some of these, as in the cephalic and thoracic regions, are so 

 intimately united that the divisions cannot be traced, except in the 

 embryo. In adults the thoracic segments are further modified, for 

 great extension and concentration of force, by expansions, primarily, 

 of the aerating apparatus into legs, wings, or other appendages. In 

 short, the thoracic region is evidently the concentration of the life of 

 these creatures. 



Now to advance beyond this type. Nature never changes her tools 

 — her means; and even her plans present but slight modifications. 

 Her collection and concentration of energy in the thoracic region of 

 polysegmental annulosa is a gathering of her strength at that point 

 whence the next march will begin. 



Exactly as we may see an individual segmentarian zoary doubling 

 itself up for its own comfort, increase of heat, or of force — exactly as 

 we have seen in vegetal life, after a longitudinal or a superficial evolu- 

 tion of the elements of the compound, energy concentrated by a fold- 

 ing down of the compound upon itself, and an adhesion — so works 

 Nature here. The concentration of life or force at any one point di- 

 minishes its intensity in remoter segments ; a more intimate union of 

 a few segments causes atrophy in the more distant frontier provinces ; 

 and this process continues, in fact, until the segments are reduced to 

 two. The very fact of a closer folding and adhesion of two would 

 have this result. This is a position we might, at this stage, compre- 

 hend a priori. Now let us see if it has any foundation in fact. 



Again I repeat, this is not an imaginary process I am going to amuse 

 you with — it is not speculation — but an irrefragable chain of facts and 

 demonstrations. The entomostracous group of Crustacea affords us 

 illustrations of every step of the progress. First, an excessive devel- 

 opment of two segments of the thorax ; then, atrophy or dwarfing of 

 the cephalic and abdominal regions, in various degrees. In cypris, for 

 instance, two segments are so enormously developed as to usurp the 

 mass of its substance, if not yet all the functions of its life. The dor- 

 sal scales of these two segments are actually so enlarged as to present 



