ADAPTATION TO SURROUNDINGS 79 



Summary of the Study of Crayfishes 



To summarize your study, write a connected account of 

 the relations of crayfishes to their environments, under 

 the following topics : — 



1. What are the varying conditions in their surroundings 

 which crayfishes must meet ? Which are most important ? 



2. What conditions must be maintained in order that 

 crayfishes may succeed, i.e. may live and reproduce ? 



3. How does a crayfish know what are the conditions 

 around it ? 



4. How is it fitted to meet these conditions ? (Answer 

 in the following details) : — 



a. How wide a food range has it, i.e. how many kinds 

 of food does it eat? How does it find its food? How 

 does it reach it ? How does it take its food ? How does 

 it make food small enough to be eaten ? 



b. What are the organs for taking in oxygen ? Where 

 are they ? How are they attached ? How is the supply 

 of oxygen kept up ? How are the organs kept from dry- 

 ing, from clogging, and from mechanical injury ? 



c. What ranges of temperature can crayfishes endure ? 

 What temperature is best ? How do they avoid fatal ex- 

 tremes ? 



d. What are the enemies of crayfishes? What protec- 

 tion against these have they ? 



e. How often do crayfishes reproduce ? About how 

 many times during a normal lifetime ? About how many 

 eggs are there and how many of them hatch? What care 

 is given to the eggs and to the young ? About how many. 

 of the young reach maturity ? {^Suggestion. Do the cray- 

 fishes of a region vary noticeably in numbers from year to 

 year ?) 



