Relation of Higher Animals to Man 



547 



dermis of a longitudinal tract that sinks inward to become the 

 central nervous system. Next, three epidermic involutions 

 of tissue sink inward round the head region tojorm in almost 



Sacf^t 



\Suji)ef?nan. 



Croio 



(eps 



Cuttlefcsh 





drac^iic^ 



/Tio/luscs 



Procb(irtApo/>o</s 



Fig. 27 — Diagram to show comparative taxonomic and biologic relation 

 of higher animals. 



invariable order of appearance (1) the olfactory tissue or spe- 

 cial chemo tactic center, ('2) the optic tissue, or special heliotactic 

 center, (3) the auditory tissue or special tonotactic and geotac- 

 tic tissue. Later other epidermal modifications, already re- 



