THE ORIGIN OF VERTEBRATES. 163 



organ of assimilation and growth, the mouth, or opening of the 

 digestive cavity ; for the primitive coelenteron was Httle more 

 than a food-bag. 



So in the h.igher animals — in the annelids, or worms, we 

 find a dorsal central ganglion ; that is, a nerve mass, in the upper 

 part of the head, and a ventral gangliated chain extending on 

 the underside throughout the length of the animal; in the 

 arthropods, a central dorsal ganglion, referred to in this work 

 as " supra-(iesophageal." or above the gullet, and an " infra-oeso- 

 ])hageal " ganglion. IJetween these two ganglia in the head of the 

 arthropod lies the stomach, called, from its position in the head» 

 the " cephalic stomach." " Arthropods,'' it may, perhaps, be 

 explained, is the name given to the large order which includes 

 Crustacea (lobsters, crabs, king-crabs, etc.), scorpions, spiders, 

 and insects. 



The continual expansion and development of the nervous 

 system consequent upon evolutionary progress leads to pressure 

 upon the digestive organs which it surrounds ; and the arthropod 

 animal finds itself faced with an increasingly perplexing pro- 

 blem. The development of the brain is necessary to enable it 

 to adapt itself to its environment; but the stomach and de- 

 pendent digestive organs cannot well be dispensed with if the 

 animal is to repair the bodily waste and carry out its functions. 



It would seem, however, that the nervous and digestive 

 systems which should have been mutually lielpful, were, by the 

 exigencies of space in the head and thorax, thrown into a posi- 

 tion of antagonism; it became a question of fighting for "head- 

 room '" ; and, in the struggle that must apparently have ensued, 

 victory or defeat would have been equally fatal to the perpetua- 

 tion of life in this class of organisms. 



■ '•Something had to be done [says Dr. Gaskell]. Some way had to 

 I;e found out of this difficulty." 



The situation certainly seems extraordinary ! But the way 

 out suggested by our author is not less remarkable. It is as if 

 an All-\Mse Providence had said : " Bless me ! I am working 

 on wrong lines altogether ! I must make another try ! " But 

 this fresh " start " entailed a radical change in design ; for the 

 threatened atrophy of the brain 



" meant degeneration and reduction to a lower state of organization ; 

 while on the other hand the further development of the brain necessitated 

 the establishment of a new method of alimentation or feeding.'"* 



Lamartine describes how the great Architect of the 

 Universe 



" D'un pied dedaigneux le lan<^ant, dans I'espace, 

 Rentra dans son repos." 



P.ut. if Dr. Gaskell's hypothesis is accepted, it is plain that that 

 attitude has to be abandoned in order to prevent a break-down. 



*0p. cit, p. 57. 



