292 



CIVIC BIOLOGY 



called " Brooks's Law of Extermination of Species by Man." Stated in 

 his own words, this law is " To marine food fishes man is a catastrophe, 

 not a natural enemy" This means " Man takes the adults which natural 



enemies have spared to con- 

 tinue the species." Figs. 133 

 and 135 show this law diagram- 

 in atically as it applies to the 

 Adult period,4O(?) lobster. It is applicable to 

 one pair ~ evel T species that man attacks, 

 from oysters and lobsters to 

 whales and pine trees. When 

 man disturbs the nice balance 

 of nature he must assume 

 control ("have dominion") 

 or lose the species. 



Blue crab Cattinectes sapi- 

 dus. This common crab of the 

 Atlantic-coast markets ranges 

 from Massachusetts Bay to 

 Mexico, and, while it is taken 

 by millions every year, shows 

 as yet no alarming signs of 

 decrease. Two facts in the 

 natural history of the species 

 may largely account for this : 

 the eggs are minute, a female 

 laying on the average more 

 than 3,000,000 at a batch ; and, 

 while molting, each female is 

 protected by a hard-shelled 

 male. 



Pacific crab Cancer magister. 

 This robust crab, 7-9 inches 

 broad by 4-5 inches long, 

 ranges from Alaska to Lower 

 California. In the markets of 

 the Pacific it supplies the place 

 of both the lobster and the 

 blue crab of the Atlantic. 

 State laws are beginning to 



Lobster ling per ioil, 



6 years; 200 V 



2 individuals 



Larval (critical) 

 period, 1 month; 

 2,000,000 > 200 



idividuals 



FIG. 135. Diagram representing the indi- 

 viduals at different stages in a generation 

 of lobsters 



This is another form of expression of Brooks's 

 law. The typical form is a pyramid, with 

 a broad base of eggs and young maintained 

 by a small apex of adults. Each species of 

 animal or plant has a form of its own de- 

 pending on number of eggs and duration of 

 the different stages. The large number of 

 eggs, the long life of the adults, and the 

 extreme reduction of numbers in the short 

 critical, larval stage reduces the typical 

 pyramid in the case of the lobster to a 

 monument with a broad base of eggs which 

 shrinks suddenly during the larval stage to 

 a slender spire representing the adults 



