CHAP, in.] OF MOVEMENTS IN THE ANIMAL KINGDOM. 351 



state, that of the amoeba, for example ; then the cellular form ; 

 finally the form in tubes. According to a certain number of 

 histologists and physiologists, there is under all these varied 

 forms an identical substance. Doubtless the form can be 

 dominated by the essence and the same organised substance 

 may, strictly, constitute anatomical elements diversely configured. 

 Nevertheless, almost always, the morphological differences corre- 

 spond to functions more or less dissimilar. Even the diverse 

 varieties of figurate muscular elements have each, as we shall 

 see by and by, their special mode of contractility. As to the 

 amorphous contractile substance, we can, at the most, only con- 

 sider it as a first outline of the muscula'r element. It is semi- 

 fluid, coagulates at 40 degrees, while the true muscular substance 

 is solid. We can bring it into affinity with the semifluid and 

 vitreous substance contained in the large contractile cells of 

 the hydras, and also with the substance which constitutes first 

 of all the heart of the vertebrated embryon. 1 



It is only in the form called fibro-cellular that the muscular 

 substance acquires a veritable autonomy. It is then represented 

 by fusiform cells, more or less flattened, provided with one or 

 two Duclei and capable of compressing or of swelling themselves 

 out by contraction. There are often fine granulations round 

 nucleus. The length of the fibre-cell can vary from some hun- 

 dredths of a millimetre to half a millimetre. These fibro-cells 

 are found in great number in man and in the mammifers, in the 

 muscular coats of the intestine, of the veins, and of the arteries, 

 in the excretory conduits, under the skin in diverse regions, 

 especially under the pilose follicles, which they put in move- 

 ment, under the scrotum, and so on. This type of contractile 

 element is found with variations in all the vertebrates, and 

 in a great number of invertebrates. In both cases it usually 



1 Recently it has been pretended that the sarcode is semifluid, even in the 

 striated muscular fibre, and that this substance is contained in tubes. And it 

 has been said that a dermatoid was seen marching in every direction in the 

 very heart of a muscular fibre as if in a liquid. 



