NOTES. 393 



149 The antennae are more probably altogether undeveloped, and the jaws 

 of the Spider correspond to the mandibles of the Lobster. 



160 Compare the single thread of the Silk-worm and other caterpillars. 



151 The common Spider, peira, which constructs with almost geometri- 

 cal precision its net of spirals and radiating threads, will finish one in forty 

 minutes, and just as regularly if confined in a perfectly dark place. 



152 These parts do not correspond to the parts so named in human anatomy. 

 See also p. 1G2. 



153 The pupa-case is often ornamented with golden spots in Butterflies ; 

 hence the common name, chrysalis. 



154 In aquatic animals the posterior limbs are the ones aborted or reduced, 

 if any ; in land animals the fore-limbs are usually sacrificed. 



155 The smallest corpuscles are found in Ruminants ; the largest in Am- 

 phibians with permanent gills. The average size in Birds is double that in 

 Man, and about equal to that in the Elephant. Those of Monkeys are a 

 trifle smaller than the human. In the embryo they are larger than in the 

 adult. Camels only among Mammals have oval disks. 



156 The facial angle becomes of less and less importance as we go away 

 from man, and for two reasons. Where the brains do not fill the brain-case 

 the angle is obviously of little value, and if the jaws are largely developed the 

 angle is reduced, although intelligence may not be altered. 



" 7 Oblong human skulls, whose diameter from the frontal to the occipital 

 greatly exceeds the transverse diameter, are called dolichocephalic ; and such 

 are usually prognathous, i. e., have projecting jaws, as the negro's. Round 

 skulls, whose extreme length does not exceed the extreme breadth by a 

 greater proportion than 100 to 80, are brachycephalic ; and such are gener- 

 ally orthognathous, or straight-jawed. 



158 The classes are variously grouped into the Hcematocrya, or Cold- 

 blooded, and the Hcematotherma, or Warm-blooded ; into the Branchiata 

 and Abranchiata ; into the Allantoidea and Anallantoidea. 



159 It would be safe to say that any living Vertebrate with side fins sup- 

 ported by fin-rays is a Fish ; but the extinct Reptile Ichthyosaurus also had 

 them. 



HO Tne ca p a city for growing as long as life lasts, which some Fishes are 

 said to possess, may be explained by the facts that their bodies are, firstly, of 

 very nearly the same specific gravity as the water in which they live, and, 

 secondly, of a temperature which is but a very little higher than that which 

 they are there exposed to. Thus the force which in other animals is ex- 

 pended in the way of opposition to that of gravity and in the way of pro- 

 ducing heat is available for sustaining continuous growth." ROLLESTON. 



m Amphibians with a moist skin are also remarkable for their cutaneous 

 respiration. They will live many days after the lungs are removed. Their 

 vertebras vary in form : in the lowest they are biconcave, like those of Fishes ; 

 in Salamanders they are opisthoco3lous : in the Frogs and Toads they are 

 usually procoelous. 



169 Salamanders are often taken for Lizards, but differ in having gills in 

 early life and a naked skin. The Froteus and Siren resemble a tadpole ar- 

 rested in its development. 



