92 



The Insides and the Workings of Living Things 



the brain and the nervous system and the special sense organs, 

 to the digestive system and to the muscles. It extends even 

 to the reproductive organs, although the fishes generally lay 



their eggs in the water 

 and abandon them, the 

 reptiles and birds lay eggs 

 and make more or less 

 provision for the young, 

 and mammals carry the 

 embryo to a relatively ad- 

 vanced stage and then 

 suckle the young. The 

 neck of the giraffe has 

 the same number of ver- 

 tebras as the neck of the 

 mouse; the leg of the 

 stork repeats bone for 

 bone the leg of the spar- 

 row. 





Fig. 24. Homologies among the 

 Appendages of the Lobster 



In the Crustacea all the appendages are built 

 on the same plan, but each segment of the body 

 (represented by Roman numerals) may have a 

 pair of distinctive organs. / and II are sensory; 

 III—V combine sensory functions with food- 

 getting; V7-VJ// are chiefly food-getters, but 

 are also related to breathing; 7X is the nipper; 

 X and XI are both grasping and locomotor 

 organs; X/7 and X77/ are walking legs. The 

 abdominal appendages X7V-XV777 are called 

 swimmerets and probably assist in slow swim- 

 ming. X7V and XV are also related to reproduc- 

 tion in the male, and in the female all the 

 swimmerets carry the hatching eggs and larvae. 

 X7X and XX spread out into a flat tail-paddle, 

 used in swimming backward suddenly. From 

 Gruenberg, Biology and Human Life, published 

 by Ginn & Company. 



Jaws and Claws 



The arthropoda, 

 which show a very re- 

 markable degree of spe- 

 cialization among the 

 higher members of the 

 group, also yield an im- 

 pressive array of varia- 

 tions upon identical 

 themes. Among the lob- 

 sters and crayfish (Deca- 

 pods) the abdomen is 

 seen to be segmented, like 

 the body of a grasshopper 

 or wasp. Each segment 

 carries a pair of append- 



