CoGiTic Evolution of Man 619 



small group of nerve cells as in medusae or echinoids, or by 

 localized ganglionic enlargements as in the earthworm, or by 

 special areas of the spinal cord or lobes of the highly differenti- 

 ated brain as in dogs, guinea pigs, etc. But it is when the 

 ganglionic masses become more and more concentrated in, and 

 correlated or summated by, the enlarging brain that instincts 

 merge into intelligence. So, while in the groups Cephalopoda, 

 Arachnida, Insecta, Aves, and in the lower Mammalia (p. 545) 

 the more primitive members of each group show rather feeble 

 instincts, as one rises through evolving genera of each group a 

 stage is reached when the instincts become so condensed and 

 correlated into summated resultants that such deserve fully 

 the appellation intelligence. 



We have aheady stated that such advance is correlated with 

 increased condensation of the nerve centers, while both are 

 dependent on and are an outcome of rapid transfers of afferent 

 and efferent stimuli through highly specialized organs acces- 

 sory to and around the brain, such as antennae, trunk, or arms. 

 In this connection we need merely draw attention once more 

 to Edinger's diagrams of brain increase, and specially of cere- 

 bral increase, in transition from fishes to man (p. 240). As to 

 the degree of intelligence shown by higher invertebrates and 

 the lower vertebrates, Holmes in Chapters X and XI of his 

 work (183) has ably discussed the question, though the writer 

 inclines to consider that he has — possibly with commendable 

 caution at the present stage of our knowledge — rather under- 

 estimated intelligence, and overestimated instinct in some 

 groups, notable the higher insects. 



But in the process of neural growth and condensation an 

 important feature is that the sense-percej^tors develop, from 

 the Rotifera and Turbellaria upward, nearly always in definite 

 order, and in certain ratios of sense importance. Thus even 

 in Rotifera, but particularly from these upward along the tur- 

 bellarian, nemertean, cyclostome, and apodous line up to man, 

 after the first foundations of the nervous system have been 

 laid down the olfactory, the optic, and the audito-geotactic 

 sense receptive centers appear in named succession. The 



