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CHAPTER XXII 



VEBTEBBATED ANIMALS 



WE are now arrived at the highest division of the animal kingdom, 

 in which the bodily fabric attains its greatest development, not only 

 as to completeness, but also as to size ; and it is in most striking 

 contrast with the class we have been last considering. Since not 

 only the entire bodies of vertebrated animals, but, generally speak- 

 ing, the smallest of their integral parts, are far too large to be viewed 

 as microscopic objects, we can study their structure only by a 

 separate examination of their component elements ; and it seems, 

 therefore, to be a most appropriate course to give under this head a 

 sketch of the microscopic characters of those primary tissues of 

 which their fabric is made up, and which, although they may be 

 traced with more or less distinctness in the lower tribes of animals, 

 attain their most complete development in this group. 1 



Although there would at first sight appear but little in common 

 between the simple bodies of those humble Protozoa which con- 

 stitute the lowest types of the animal series, and the complex 

 fabric of man or other vertebrates, yet it seems certain that in 

 the latter, as in the former, the process of * formation ' is essentially 

 carried on by the instrumentality of protoplasmic substance, univer- 

 sally diffused through it in such a manner as to bear a close resem- 

 blance to the pseudopodial network of the rhizopod ; whilst the 

 tissues produced by its agency lie, as it were, on the outside of 

 this, bearing the same kind of relation to it as the foraminiferal 

 shell does to the sarcodic substance w r hich fills its cavities and 

 extends itself over its surface. For, as was first pointed out by 

 Dr. Beale, 2 the smallest living * elementary part ' of every organised 



1 This sketch is intended, not for the professional student, but only for the 

 amateiir microscopist who wishes to gain some general idea of the elementary struc- 

 ture of his own body and of that of vertebrate animals generally. Those who wish 

 to go more deeply into the inquiry are referred to the following. The translation of 

 Strieker's Manual of Histology, published by the New Sydenham Society ; the 

 translation of the 4th edition of Professor Frey's Histology and Histo-Chemistry of 

 Man ; the ' General Anatomy ' of the 10th edition of Quoin's Anatomy, 1893, by 

 Professor Schafer; and the Atlas of Histology, by Dr. Klein and Mr. Noble Smith. 



2 Professor Beale's views are most systematically expounded in his lectures On the 

 Structure of the Simple Tissues of the Human Body, 1861 ; in his How to work 

 with the Microscope, 5th edition, 1880 ; and in the introductory portion of his new 



