252 THE MICROSCOPE AND ITS KEVELATIONS. 



CHAPTEE XX. 

 VEKTEBRATED ANIMALS. 



648. WE are now arrived at the highest division of the Animal King- 

 dom, 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 speaking, the 

 smallest of their integral parts, are far too large to be viewed as Micro- 

 scopic objects, we can study their structure only by a separate examina- 

 tion 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 For some time after Schwann first made public the remark- 

 able results of his researches, it was very generally believed that all the 

 Animal tissues are formed, like those of Plants, by a metamorphosis of 

 cells; an exception being taken, however, by some Physiologists in regard 

 to the 'simple fibrous' tissues ( 668). There can be no longer any 

 doubt, however, that this doctrine must be greatly modified; 2 so that, 

 whilst the Vegetable Physiologist may rightly treat the most highly organ- 

 ized Plant as a mere aggregation of cells, analogous in all essential par- 

 ticulars to those which singly constitute the f unicellular ' ProtopJiytes 

 ( 227), the Animal Physiologist does wrong in seeking a cellular origin 

 for all the component parts of the Animal fabric; and may best interpret 

 the phenomena of tissue-formation in the most complicated organisms, 

 by the study of the behavior of that apparently-homogenous ' protoplasm ' 

 of which the simplest Protozoa are made up, and by tracing the progres- 

 sive ' differentiation ' which presents itself as we pass from this through 

 the ascending series of Animal forms. 3 



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

 amateur Microscopist, who wishes to gain some general idea of the elementary 

 structure 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 as the 

 most recent and elaborate Treatises that have appeared in this country: The 

 translation of Striker's "Manual of Histology," published by the New Sydenham 

 Society; the "Handbook for the Physiological Laboratory," by Drs. Burdpn- 

 Sanderson, Michael Foster, Brunton, and Klein ; the translation of the 4th edition 

 of Prof. Frey's " Histology and Histo-chemistry of Man;" the ' General Anatomy ' 

 of the 8th edition of " Quain's Anatomy" (1874); and the "Atlas of Histology," 

 by Prof. Klein and Mr. Noble Smith (1880-1). 



2 The important 'Review of the Cell-Theory,' by Prof. Huxley, in the "Brit, 

 and For. Med.-Chir. Review," Vol. xii. (Oct, 1853), p. 285, may be considered the 

 starting-point of many later inquiries. 



3 The study of Comparative Histology, prosecuted on this basis, promises to be 



