39- 



They are nicely balanced against each other and any stimulus which 

 upsets the balance by adding to the strength of one factor or taking 

 from the strength of another factor results in a more or less radi- 

 cal change in the behavior of tne animal. It is often difficult, 

 moreover, to discern the cause of a change in behavior, eo delicate 

 is the balance between the different factors, and so impossible is 

 it to keep track of the changes of fatigue, hunger, etc*, that play 

 an important part in the relative irritability of the animal as a 

 whole, and of its different parts from time to ti;ae. An analysis 

 of the behavior of starfishes, based upon observations and experi- 

 ments on only four or five species, can not pretend to completeness 

 or to a generality covering the whole group of Aateroidea* (See 

 kangold 1908 on the self burying reaction of Astropefltfpl* 

 Theories ojf the moohaniap gjf coordination.* 

 It is probably true that all starfish locomotion involve! 

 in some of its phases at least a "unified impulse" among the tube 

 feat in various p-arts of the body* 



The mechanism of such coordination is of course very com* 

 p lex. As cording to Von Uexkull, vn the sea urchin it involves the 

 functioning of many nerve nets, connecting and supplying with simi- 

 lar "quantities" of "tonus" homologous parts of the various coordi- 

 nating organs (tube feet, spines etc.,). Pending adequate histolog- 

 ical investigations it would be well to state as an hypothesis that 

 since homologous parts of coordinated tube feet act in almost ex- 

 actly the same manner they are probably connected by nervous paths 

 of lower threshold than are non homolgous parts* 'Hie value of such 

 speculation, however, is dubious, and it is better to keep within thi 

 data of physiology in evaluating the coordinated impulse, since the 

 morphological data is wanting* 



