2i8 The American Geologist. October, i90i. 
and furnished an unlimited food supply to the somehow rap- 
idly advanced type of crustacean life.* 
Granted that the food supply was abundant Semper's 
statement directly applies. He says (p. 65) "it .is self-evident 
that an optimum of nutrition can alone insure the 
normal functions of all the organs ; if it does not 
attain the optimum, the functional activity of all the 
organs is impaired; modifications at the same time occur 
in their structure, i. e., the animals grow leaner because in- 
capable of exercising their sexual functions, etc." The sex- 
ual powers of the Cambrian trilobite so far as food strength- 
ened or increased them were probably well developed. 
Temperature was propitious. It has been over and again 
demonstrated that warmth vitalizes the generative functions. 
There is a wide range of differing capacitv in this respect in 
animals, and the familiar term enrythermal has been applied 
to those organisms which endure contrasted temperatures. 
But the fact is almost universal that heat is stimulating 
and helpful, to animal life and its functions. It has been ob- 
served that snails of the warm Mediterranean region are 
quickly brought to sexual maturity and that "species of the 
same genera, perhaps even the same species, in damp and 
cold climates do not produce a new generation vmtil they are 
fully grown while in the dry warm region of the Mediter- 
ranean they have produced two generations "before they are 
fullv grown" (Semper). Semper has himself observed that 
the larvje of Branchipus and Apiis hatched out in less than 
twenty-four hours at a temperature of 30° Cent., but at i6°- 
20° they required some weeks. 
Today our shore crustaceans require the warmth of sum- 
mer to bring their powers of fecundation into activity, but it 
can readily be understood that the Cambrian trilobite in an 
equable and hot climate, such as in all probability, and, as 
almost universally recognized, prevailed at that period, may 
have excluded two broods or more in the seasonal year, while 
the rapidity of development of the larvae into mature forms, 
and their early acquirement of sexual activity may have still 
*The omnivorous propensities of the modern crayfish, hare been character- 
■ Tzed by Huxley, "few things in the way of food are amiss to the crayfish ; liv- 
idg or dead, fresh or carrion, animal or vegetable, it is all one." Trilobites are 
not crayfish, but it is reasonable to infer that the elements of nutrition iu the 
whole group of Crustacea are not dissimilar throughout. 
