THE AETHEOPODS 367 



(5) The antennary glands of crayfishes do the work of kid- 

 neys of frogs in eliminating nitrogenous excretions. 



(6) The nervous system presides over coordination ( 54), 

 and the special senses in both frog and crayfish. 



(7) The reproductive organs of both animals have identical 

 work; the ovaries forming ova or egg-cells, the spermaries 

 producing sperm-cells, while the oviducts and sperm-ducts 

 are simply tubes for conducting egg-cells and sperm-cells 

 to the exterior, where each egg-cell may be entered and fer- 

 tilized by a sperm-cell. 



It is evident from above account that in the bodies of a 

 frog and a crayfish the same work is necessary to the mainte- 

 nance of life-activities, and that there is a system of organs 

 for each function. In other words, the crayfish and the frog 

 both have a high degree of physiological division of labor 

 ( 269). 



However, there is one important difference; namely, 

 that the organs of the frog are much more complex and 

 more highly specialized. For example, the frog's diges- 

 tive system consists of mouth-cavity, esophagus, stomach, 

 small intestine, large intestine, pancreas, and liver; while 

 that of the crayfish consists of mouth, esophagus, stomach, 

 digestive glands, and intestine. For another, example of 

 the frog's greater complexity, we might compare its nervous 

 system with that of the crayfish. 



However, the crayfish's organs are complex enough for the 

 needs of its sluggish life. With the more highly developed 

 muscular and nervous activities of the highest backboned 

 animals is associated more specialization and complexity of 

 all organs which are essential for the individual life. The 

 great significance of this fact is impressed upon us if we 

 stop to consider that man (the highest organism) is espe- 

 cially distinguished by the complexity of his nervous organs 

 along with remarkably perfect muscular functions ; and that 

 to this development o? the nervous and muscular systems 



