272 ZOOLOGICAL PHILOSOPHY 



out nervous threads to various parts, it was henceforth capable of 

 giving rise to muscular excitation without however being able to 

 produce the phenomenon of feeling. 



From these principles I believe I am justified in drawing the con- 

 clusion that the formation of the muscular system is subsequent to 

 that of the earliest stages of the nervous system, but that the faculty 

 of carrying out actions and movements by means of muscular organs 

 is in animals prior to that of experiencing sensations. 



Now since the origin of the nervous system is anterior to that of 

 the muscular system, and since its functional existence only dates 

 from the time when it was composed of a main medullary mass from 

 which issue nervous threads, and since no such system of organs can 

 exist in animals with organisations as simple as the infusorians or most 

 polyps, it clearly follows that the muscular system is peculiar to 

 certain animals, that it is not possessed by all, and yet that the faculty 

 of acting and moving by muscular organs exists in a greater number 

 of animals than does the faculty of feeling. 



For deciding as to the presence of a muscular system in animals 

 in doubtful cases, it is important to consider whether there are in 

 these animals any points of attachment for muscular fibres, of a 

 certain strength or firmness ; for, being constantly under stress, these 

 points of attachment become gradually stronger. 



It is certain that the muscular system exists in insects and all animals 

 of subsequent classes ; but has nature established this system in 

 animals that are more imperfect than insects ? If she has, it can 

 hardly be (as far as the radiarians are concerned) anywhere but in 

 the echinoderms and fistulides : it cannot be in the soft radiarians : 

 perhaps there are rudiments of it in the sea-anemones ; the coriaceous 

 substance of their bodies makes this belief plausible, but its presence 

 cannot be supposed in the hydra nor in most other polyps, and still 

 less in the infusorians. 



It is possible that, when nature set out to establish some special 

 system of organs, she selected conditions favourable to their creation ; 

 and that consequently there are several interruptions in our scale of 

 animals near the point at which the system is established, and due 

 to the existence of cases in which its formation was impracticable. 



Attentive observation of the operations of nature in the light of these 

 principles will doubtless teach us many things that we do not yet 

 know on these interesting subjects, and may perhaps disclose the fact 

 that although nature was able to begin the muscular system with the 

 radiarians, yet the worms which follow them are still devoid of it. 



If this principle is well-founded, it will confirm what I have already 

 urged with regard to worms, viz. : that they appear to constitute a 



