1921] Riley: Responses of Water-Sirider 263 
feint is less pronounced than that of Talorchestia longicornis. 
However, its thigmotactic responses are much better developed 
than are those of Orchestia agilis. Holmes (1903, pp. 195-196) 
states that: 
The conduct of this species [Orchestia palustris] is intermediate 
between the thigmotactic response of agilis and the death-feigning of 
Talorchestia. Some specimens might almost be said to possess a death- 
feigning instinct. 
He believes that if certain of its thigmotactic responses 
were 
carried out in a more decided manner and persisted in longer [that 
they] would result in what would commonly be called feigning death 
Continuing his discussion of the probable development of 
thigmotaxis into the death-feigning instinct,he remarks that: 
The death-feigning instinct of Talorchestia is an instinct which, | 
believe, has its root in the thigmotactic responses common among 
other amphipods. One may easily conceive that by the selection gen- 
eration after generation of those individuals of O. agilis in which the 
thigmotaxis is most persistent . . . a mode of behavior like the death- 
feigning instinct of Talorchestia might readily be produced. 
It seems not improbable that an instinct having its phyletic root in 
a simple thigmotactic response may in course of time come to be com- 
paratively independent of contact stimuli. The persistence of death- 
feigning in Talorchestia depends far less upon contact than the thigmo- 
tactic reactions of the aquatic Amphipoda, although, as has been 
pointed out above, contact still increases the duration of the feint. 
Holmes points out that eventually contact stimulation may 
become necessary only to initiate the death-feigning response, 
but may not be required for the continuation of the feint. 
In course of time a mere tap or jar is all that is required to bring 
about the response. He points out that the death-feint is 
generally evoked as a response to some sort of contact stimu- 
lation. These references to the work of Holmes will be 
closed by directing attention to one other statement recorded 
by this writer. He (1903, p. 193) states that: 
Talorchestia does not feign death upon receiving purely visual 
impressions; it requires contact of some sort to elicit this form of 
response. The same fact seems to be quite general in the death-feigning 
of animals, especially below the vertebrates, and it is a circumstance, 
I believe, of considerable significance in relation to our views of the 
genesis of this instinct. 
