IO22 



VERTEBRATED ANIMALS 



microscopic examination of even a minute fragment of it. The 

 following are the average dimensions of the lacunae, in characteristic 

 examples drawn from four principal divisions, expressed in fractions 

 of an inch : 



Man . 

 Ostrich 

 Turtle . 

 Conger-eel 



Long Diameter 

 1-1440 to 1-2400 

 1-1333 1-2250 

 1-375 1-1150 

 1-550 , 1-1135 



Short Diameter 

 1-4000 to 1-8000 

 1-5425 1-9850 

 1-4500 1-5840 

 1-4500 1-8000 



The lacunae of birds are thus distinguished from those of mam- 

 mals by their somewhat greater length and smaller breadth, but 



they differ still more in the 

 remarkable tortuosity of their 

 canaliculi, which wind back- 

 wards and forwards in a very 

 irregular manner. There is an 

 extraordinary increase in length 

 in the lacunae of reptiles, with- 

 out a corresponding increase in 



FIG. 752. -Lacunae of osseous substance : breadth ; and this is also seen 

 a, central cavity ; b, its ramifications. in some fishes, though in ge- 



neral the lacunae of the latter 



are remarkable for their angularity of form and the fewness of their 

 radiations, as shown in fig. 753, which represents the lacunae and 

 canaliculi in the bony scale of the Lepidosteus (' bony pike ' of the 

 North American lakes and rivers), with w r hich the bones of its in- 

 ternal skeleton perfectly agree in structure. The dimensions of the 

 lacunse in any bone do not bear any relation to the size of the animal 



FIG. 753. Section of the bony scale of Lepidosteus : a, show- 

 ing the regular distribution of the lacunae and of the connecting 

 canaliculi ; b, small portion more highly magnified. 



to which it belonged ; thus there is little or no perceptible difference 

 between their size in the enormous extinct Iguanodon and in the 

 smallest lizard now inhabiting the earth. But they bear a close rela- 

 tion to the size of the blood-corpuscles in the several classes ; and 

 this relation is particularly obvious in the * perennibranchiate ' 

 Batrachia, the extraordinarily large size of whose blood-corpuscles 

 will be presently noticed. 



