578 Animal Biology 



Certain corresponding parts on diflferent plants appear to have origi- 

 nated from the same part of some common ancestor and to be struc- 

 turally similar. Such are known as homologous structures. For example, 

 the stamens and carpels of a flowering plant may be considered, in gen- 

 eral, to be homologous with the scalelike sporophylls (spore-bearing 

 leaves) of pine cones and the sporophylls of ferns. Pollen sacs and 

 ovules may be considered homologous with sporangia. 



.^U— 



L Temar ^^ 



Tibia 



Coxa 



Jfrochanten- 



...Mh 



Tibial J pur 

 __T(arja5 



Wasp 



Fig. 308. — Legs of insects, showing similarity of structure in different species. 



ANALOGY (a -naV o ji) (Gr. analogia, proportion) 



Analogous organs or structures are similar in junction hut are not re- 

 lated genetically and do not have a similar embryologic origin or mor- 

 phologic structure. For example, the wings of bats and butterflies are 

 analogous because they are used for flying, but they are not homologous. 



AUTOTOMY (o-tot'omi) (Gr. autos, self; tone, cutting) 



Certain organisms such as sea cucumbers, starfishes, crayfishes, lobsters, 

 etc., have the natural ability to sever (self amputate) a structure or organ 

 at a definite, predetermined point or area. This phenomenon is called 

 autotomy. In the crayfish and lobster there is a definite breaking point, 

 varying with the appendage, and a new one similar to the lost one 

 develops from the remaining portion. In certain crustaceans the ap- 

 pendage is flexed by muscles until it breaks at its breaking point. After 

 the appendage is thrown off, a protective membrane is formed at the 

 site of the injury to prevent hemorrhage until regeneration is accom- 

 plished. 



