64 



LUCERNARI^ AND THEIR ALLIES. 



128. Nervous System Formless.— BcjonA this indication of the eye-spots we have 

 not discovered the least trace of anything that could be assigned to the nervous 

 system. Tlie remarkable regularity with which the cells of each wall of the body 

 are disposed renders every step in a survey a positive advance in the knowledge of 

 their histological relations; and we feel assured that no combination of strata and 

 no assemblage of cells was ever more thoroughly studied, and we doubt if, but 

 rarely, they ever received so much attention. If, then, there is a nervous system 

 with a form, it must constitute a part of what we have described as the muscular 

 system. This is a mere suggestion, and has no real basis, except that the muscles 

 have a fibrous structure, and, as a bare possibility, might include among themselves 

 nervous threads of a similar form. We know that it is no uncommon difficulty to 

 determine, in some animals, Avhat is nervous and what is tendinous or unstriped 

 nuiscular fibre, but seldom do these barriers arise from their intermingling in one 

 common stratum, or trending in parallel lines with each other. Much less do they 

 originate from an impossibility to distinguish the one from the other, when they 

 can be subjected to the highest powers of the microscope. This is our ground for 

 assuring ourselves that there is no nervous system, having a form, intermingled 

 with the muscular mass. That it has a potential existence, there can be no doubt, 

 and that it can transfer sensations from the remotest points of the periphery of the 

 body to its centre no one will deny upon seeing the tips of the tentacles convey 

 some miniature victim to the mouth. Along what lines these sensations and volitions 

 are propagated it is not possible to determine, but it seems to us more likely that 

 interstitial cyioblastema should be the medium than that cells which are already 

 appointed to the formation of a wall or a tissue should perform a double duty. 



129. Cytohtastema. — In the lowest ranks of life, it is the amorphous cytoblaste- 

 matous substance that prevails, that even constitutes the whole body, as every 

 student of the lower Protozoa is well aware. The Amoeba, Diffiugia, in fact all 

 Rhizopoda, are moving, sentient masses of cytohlastema. The velocity of retraction 

 of a pscudoixxllum of a Rhizopod cannot be surpassed by the most highly developed 

 muscle of a Vertebrate. The consciousness with whicli a Diffiugia builds up its 

 test, bearing each grain of sand to its place in the domicile with well-defined intent, 

 is none the less an exhibition of the coursing of a nervous current through its 

 homomorphous, cell-less mass, than is that of the Phrygancan larva, with abundant 

 striated muscles and sharply segregated nervous cord and fibres, building up its 

 caddice-case, with all the ingenuity of a human basket maker. The cells which 

 form the elements of a system, whether nervous or muscular, are not so much the 

 necessary concomitants of the function which is to operate along certain lines, as 

 the indicators of the outlines of the differentiation process— the guide posts, one 

 miglit say, to prevent the nervous couriers from losing their way, and straying off, 

 diffusing themselves in unknown regions of cytohlastema. The comparative difi'use- 

 ness of the nervous centres in the middle ranks of Invcrtebrata prepares us for a 

 still greater indefiniteness in the lowest grades ; and we should not be surprised to 

 hear of any one coming to the conclusion that in the latter there are no main centres 

 of dispersion and reception of nervous power and sensation, but that they are as 

 well displayed at one point in tlie body as at anotlier, and from thence propagate 



