ON THE BEHAVIOR AND REACTIONS OF LIMU- 

 LUS IN EARLY STAGES OF ITS DEVELOP- 

 MENT.' 



By Raymond Pearl. 



Introduction. 



In morpholo<Tica] research two modes of procedure are 

 usually followed in iiivestig".iting the significance of some par- 

 ticular structure of an ori^anism. First the forn). position, re- 

 lations and ot-ier characteristics of the structure in the adult 

 organism are studied. Then the embryological history is 

 worked out for the purpose of ascertaining how the structure 

 develops to the complex condition of the adult. In this way, 

 of course, has been gained the complete explanation of many 

 organs and structures which were inexplicable when the adult 

 condition alone was considered. Indeed, embryological study 

 has come to be considered an absolutel)- necessary part of 

 almost any morphological investigation which aims at complete- 

 ness. The ontogenetic history of an organ is regarded as of 

 prime importance in elucidating the adult condition. 



It is evident that the same thing may be true when the 

 problem under consideration is one in animal behavior, instead 

 of in animal morphology. As we go up the scale from the 

 lower to higher forms, the behavior becomes more and more 

 complex, and less easily resolvable into simple component 

 factors. To be sure, the increase in physiological complexity 

 does not run exactly parallel to the increase in morphological 

 complexity, yet one does not have to go far before the analysis 

 of the behavior of the adult organism becomes extremely diffi- 



' Contributions iVom the Zoological Laboratory of the University of Michi 

 gan, Ann Arbor, Mich., No. 71. 



