1917J Estcrljj: Specificity in Bdmvior 383 



evidence, as does mine (Esterly, 1912) on the copepods. Speeitieity 

 appears even more strikingly in the laboratory responses of different 

 forms. It is ontside the purpose of this paper to enter into generic 

 differences, bnt it may be said that the representatives of each of 

 five genera of copepods are nni()ue in their behavior as compared 

 with the others; the chaetognath, Sagitta hipunctata, and a schizopod 

 have also their peculiarities. 



The existence of specificity in behavior as well as in structure lias 

 not received the attention it deserves. Walter (1907) has ably pre- 

 sented the matter and the papers of Shelford (1911, 1912, 1914, 1915) 

 deal with the same topic, at least incidentally. Alice (1912, 1913) 

 also has had this point in mind, apparently. Though these writers 

 have not dealt with plankton organisms, they have shown that the 

 general principle holds in other forms. 



As regards the plankton group in particular, 1 know of no work 

 tliat has dealt with the reactions of various forms with a view to 

 ascertaining specific or generic modes of response. One gets the 

 impression from Loeb's papers (for example, Loeb, 1908, p. 732; 

 1913, p. 480) that the results from a few forms are applicable in 

 general to the plankton. It is doulitful if we can rightly conclude 

 that the reactions of any species of a genus are typical of the others 

 until the comparison has really been made. Bauer (1909, p. 80) 

 was of this opinion to a certain degree when he wrote that through 

 experiment 



Ich hoffe ... zu zeigen, (lass die Meelianismen der Tiefeiiregulierung bei den 

 verseliiedenen Formen reelit verschiedene sind und dass die beispielsweise fiir eiiie 

 Daphnidenform festgestellte Reaktionsweise nicht einnial fiir andere Art der- 

 selben Familie, gesclnveige deim fiir alle Planktonformen, verallgemeinert werden 

 kaiin. 



My results lead me to extend Bauer's statement to species of the 

 same genus. The basis for comparing the reactions of two species in 

 the same gemis is afforded in the copepods Acartia tonmi Dana and 

 A. clausi Giesbrecht. There can be no doubt of the generic identity 

 of these forms nor of their specific distinctness. Tonsa belongs to 

 one general division of the genus, clausi to the other (Steuer, 1915). 

 The two occur at La Jolla together during some seasons of tlie year, 

 and they are obtained in large numbers even in the same collections. 

 Such conditions offer unusually favorable opportunities for compari- 

 sons. No amount of experiment, however, would tell us that tonsa 

 occurs both summer and winter, while clausi appears off the station 

 pier about the first of November. This in itself shows a specific differ- 

 ence that knowledge of the animals in nature alone can supply. It is 



