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cleus. lu oviparous vertebrates, on the contrary, be- 

 sides the colouring and the membranous parts, the red cor- 

 puscle has a most distinct nucleus. And this very remark- 

 able difference of structure is the most fundamental one 

 between the Mammalia and oviparous vertebrates. Thus the 

 lecturer distinguishes these two great sections as 

 Pyrencsmata and Apyrenamata, and declares that the 

 shortest, most fundamental and universal single diagnostic 

 character of Mammalia is Vertebrates with non-nucleated 

 red corpuscles of the blood.. There are two orders of facts 

 in such inquiries, differing much in their value, j udged by their 

 significance, under the light ofourstUl limited knowledge ; the 

 one set of facts minor, incidental, and isolated ; the other large, 

 constant, and central, and worth hundreds of the former as 

 comprehending them all. Of these former, examples are 

 such as occur in the curious deviations in the shape of the 

 red corpuscles of the camels and certain fishes ; of the latter 

 facts, which appear witb the dignity of central phenomena, 

 that ofthe constant difference of structure between thePyrena;- 

 matous and Apyrensematous red corpuscles is an important 

 exemplification. The whole of " this vexed question of a 

 nucleus " affords a very curious and interesting chapter in 

 physiological history ; but the facts, often mistaken, denied, 

 asserted, and confused, are now proved and placed at the 

 service of systematic zoology. 



And thus we have shown that the red corpuscles are so 

 important, and so intimately related to the rest of the 

 organization, as to form an essential and fundamental part 

 of the anatomy of every species of the vertebrate sub- 

 kingdom, never, consequently, to be disregarded in their de- 

 scription and classification, and these corpuscles affording, in- 

 deed, by their structure, at once the most certain and central 

 difference between the two great divisions of that sub-king- 

 dom. Whenever an aberration of the size of the redcorpuscles 

 occurs in a species— e. g. Cercoleptes, Basaris, Hyrax — 

 that species will certainly prove an aberrant one in other 

 parts of its organization ; as shown too by their magnitude 



