ON THE PRINCIPLE OF CEPHALIZATION. 175 



reminds us of a parrot's beak, or that of certain oiher verte- 

 brates. Thus we have cephalic power manifested in the 

 mechanical action of the foot. 



1st, Lameliibranchs — Locomotion. 



2d, Gasteropods — Locomotion, Prehension. 



3d. Cephalopods — Locomotion, Prehension, and Ag- 

 gression. 



According to the principle of Cephalization, cephalic 

 power is manifested either as a mechanical, sensorial, or 

 psychical force. Thus the Cephalopods possess in the 

 greatest measure, all three ; while Gasteropods, not indica- 

 ting, to any great extent, aggressive action, maybe said to 

 manifest but little psychical power ; and the Lamellibran- 

 chiates manifest essentially only mechanical action. 



We have based the preceding considerations on the com- 

 mon structure of each class, and for comparison have 

 given an archetype, as it were, of each class (Series I). 

 In continuing these archetypal figures, as illustrating the 

 relative diameters and mean forms for each class (Series 



II and III), and also the mean, or average position in na- 

 ture of the antero-posterior axis (Series IV), we obtain 

 singular features of polarity,* which I will now proceed to 

 indicate; premising, however, that what follows is offered 

 with reluctance, as I have not at present the opportunity 

 to verify the statements as I would wish. In Series II 

 the average lateral form of each class is given. In Series 



III a transverse section is given of the same figures in 

 Series II. In Series II the arrow A indicates the direction 

 of anterior pole, and D indicates the dorsal region in Series 

 II and III. In Series IV a line for each class is given, re- 

 presenting the average position of their antero-posterior 

 axis in nature (A, anterior pole, P, posterior pole). The 

 central figures in Series II, III, and IV represent cor- 

 responding views of the Monomyarians. In the Polyzoa, 

 (Series II, P) the sac is long and cylindrical, the mouth 

 and anus terminate at the posterior pole, and the tentacles 

 surround the mouth only; the anus terminating outside 

 the lophophore. Witness in the highest order of Ceph- 

 alopods, the Dibranchiates, the sac as in Loligo (Series 

 II, C), long and cylindrical, and in all cases mouth and 



*We use this word in its most general sense. 



