THEORY OF REPRODUCTION. 217 



illustrated among the Hydrcmcdusa. The breakage or thinning away 

 which sets a large portion free is a katabolic process, in a sense a local 

 death. The gentleness of the gradient warrants us in concluding that 

 the liberation of sex-cells, in its earlier expressions at least, is asso- 

 ciated with a local or with a general katabolic crisis. 



V. Argument from the Close Connection between Repro- 

 duction and Death. — Without going back to primitive disintegra- 

 tions, or the asexual severance of more or less large portions, we may- 

 point further to the close connection between reproduction and death, 

 even when the former is accomplished by specialized sex-cells. We 

 shall presently discuss at greater length this nemesis of reproduction, 

 but it is important here to emphasize that the organism not unfre- 

 quently dies in continuing the life of the species. In some species of 

 the primitive annelid Polygordius, the mature females die in liberating 

 the ova. At a very different level, the gemmules of the common 

 fresh-water sponge are formed in the decay of the asexual adult, while 

 even the sexual summer forms, especially the males, are peculiarly 

 unstable and mortal. The whole history of this form seems a contin- 

 uous rhythm between life and growth on the one hand, and death and 

 reproduction on the other. Or again, the flowering of phanerogams 

 is often at once the climax of the life and the glory of death. In his 

 ingenious essay on the origin of death, Goette has well shown how 

 closely and necessarily bound together are the two facts of reproduc- 

 tion and death, which may be both described as katabolic crises. 



VI. Argument from Environmental Conditions which 

 Favor Reproduction. — The rhythm between nutrition and repro- 

 duction, or between growth and multiplication, has been as it were the 

 refrain of the preceding pages. This ' ' organic seesaw ' ' is determined 

 by the very constitution of the organism; in other words, it expresses 

 the fundamental characteristic of living matter. It is an incomplete 

 conception, however, unless it be remembered that about this " organic 

 seesaw ' ' there blows the wind of the environment, swaying it now to 

 one side, now to the other. It is important, therefore, to illustrate 

 how the play of external conditions accelerates or retards the repro- 

 ductive function. 



The influence of heat upon the reproductive powers of infusorians 

 has been carefully investigated by Maupas. The higher the tem- 

 perature up to a certain limit, the faster do these organisms reproduce. 

 In favorable nutritive conditions, Stylonichia pustulata divides once in 

 twenty-four hours at a temperature of 7 to io° C. , twice at io° to 

 1 5 , thrice at 15 to 20 , four times at 20 to 24°, and five times at 

 24 to 27 C. Illustrating the rapid rate of increase, Maupas notes 



