64 



THE AMERICAN MONTHLY 



[April, 



to certain portions of the body-sub- 

 stance, and there is actually a system 

 of definite paths formed throughout 

 the body, along which are cai'ried the 

 nervous vibrations. That there are, 

 in all low forms, systems of paths of 

 this kind which, while they are not 

 to be detected by optical or chemical 

 methods are virtually nei^ves, is evi- 

 dent from numerous observations of 

 the action of multicellular organisms 

 towards various forms of stimuli. 

 For a considerable time these tracts 

 may act vicariously, as was shown by 

 Romanes' experiments upon medusas, 

 but gradually they not only assume a 

 definite structure visible to the micro- 

 scopist, but they lose their sensibility 

 to certain impressions, and are capa- 

 ble of responding only to that form of 

 irritation to which they are most often 

 subjected. Thus, from the deposit of 

 pigment in patches upon the surface, 

 certain points become more readily 

 sensitive to light, and we have devel- 

 oped the rudiments of visual organs. 

 From the fact that the organism moves 

 habitually with a certain portion of its 

 body in advance, and this habit is seen 

 even in the amceba, this portion would 

 be more repeatedly brought into con- 

 tact with foreign bodies, and would 

 gradually develop a more delicate 

 tactile sense than other parts. 



Gradually the variously specialized 

 portions of the body become grouped 

 and centralized, and we see those ele- 

 ments mostly in the surface layers, 

 which have developed more than 

 others, their nei"vous heritage forming 

 connected groups, portions of which 

 monopolize the receptive power while 

 others are adapted for the transmission 

 of the molecular disturbance created 

 at the receptive point. 



As the acquisitions of organic mem- 

 ory become more and more abundant 

 some groups of nerve-elements lying 

 at the cross-roads of nei"vous commu- 

 nication develop their power of retain- 

 ing impressions beyond that of other 

 groups, and we have formed a senso- 

 riurn commune of some sort or other, 

 ' a nervous centre to which mediately 



or immediately,' as Spencer says, 

 ' the most heterogeneous impressions 

 are bi'ought.' Beginning with undif- 

 ferentiated protoplasm, Mr. Spencer 

 in his 'Principles of Psychology ' an- 

 nounced a priori^ and elaborated de- 

 ductively, a theory of neuro-genesis, 

 which has been found to accord with 

 the observations of microscopists and 

 embryologists. Through the labors 

 of such men as the Hertwigs, Eimer, 

 Clans, Schafer, Hubrecht, and Klein- 

 enberg, it is demonstrated that the 

 nervous system of the higher animals 

 has been gradually evolved by the dif- 

 ferentiation of the superficial cells of 

 the body. These cells, uniting by 

 their processes, produced at first a 

 supei'ficial nervous network, forming, 

 as we have seen, specialized groups 

 or sense organs, and gradually travel- 

 ling inward to give rise to the central 

 nervous system. 



There remain, however, many ques- 

 tions of interest for our microscopists 

 to settle, and the labor annually de- 

 voted to arranging diatoms and mak- 

 ing beautiful mounts of miscellaneous 

 objects would, if concentrated upon 

 these moot points, not only give in- 

 valuable results to this branch of or- 

 ganogeny, but tend to place Ainerican 

 microscopists more on a level with 

 those of Europe. 



Prof. McCalla's Nose-piece. 



The controversy that has arisen 

 between Prof. Albert McCalla and 

 Mr. W. H. Bulloch concerning the 

 invention of the ' congress ' nose- 

 piece, has made it desirable to pre- 

 sent copies of the original drawings 

 as furnished by Prof. McCalla some 

 time ago. The description is given 

 by Prof. McCalla as follows : — 



' The objective is armed with a ring 

 (fig. 13) to screw on its 

 upper end, having three 

 lugs or pins placed equi- 

 distant around its circum- 

 ference projecting hori- 

 zontally. The nose-piece 

 itself consists of an inner fixed tube 



Fig. 13. 



