494 BIOLOGY OF THE PROTOZOA 



the elaters through the activity- of nuclei which degenerate with the 

 process. In some forms the old plasmodium loses water, dries 

 and forms a hard indurated crust called a sclerotium. In the 

 majority of forms the protoplasm becomes transformed into a 

 tough skin or membrane termed the peridium which may be 

 strengthened by deposits of lime. Other parts of the protoplasm 

 become modified into felted spore capsules or capillitia through 

 which the elaters ramify. 



In all of these cases of old age protoplasm the evidence justifies 

 the conclusion that the organization has become profoundly changed, 

 the change often resulting in useful morphological and physiological 

 differentiations. The changes are of a character however which 

 prevents any recovery of vitality and death of the protoplasm 

 results unless gamete formation and fertilization supervene. 



C. Cyclical Differentiations Peculiar to Maturity. — Sexual maturity 

 in Protozoa is not a theory but a fact demonstrated in many dif- 

 ferent kinds of Protozoa. In many cases the young form slowly 

 grows to its adult condition ; differentiations appear with continued 

 metabolism until the individual becomes a gamont and gives rise 

 to gametes. Thus in polycystid gregarines the sporozoite slowly 

 grows to its definitive size and differentiations appear with that 

 growth. The protoplasmic conditions leading to gamete formation 

 may, with equal reason, be regarded as evidence of still further 

 difterentiation in the protoplasmic organization. In Schizogre- 

 garinida and in Coccidiomorpha an asexual reproductive cycle 

 intervenes betw^een the sporozoite and the gamont and the same is 

 true in the Foraminifera and the Phytomonadida. In Infusoria, 

 as Maupas long since demonstrated, fertilization is possible only 

 after a period of vegetative metabolism and reproduction. Sexual 

 maturity in general therefore, like other conditions of protoplasm, 

 may well be interpreted as evidence of specific differentiations of 

 the protoplasmic organization. 



Few problems in biology have attracted more attention than 

 those associated with sex, and attempts to interpret the phe- 

 nomenon have been as varied as they are sometimes ingenuous. 

 The very definition varies with different interpreters, the usual 

 definition involving association of the concept sex with peculi- 

 arities of structure and function which enable an observer to 

 distinguish males from females. Others regard sex as evidence 

 of a fundamental difference in protoplasm, one type giving rise to 

 males, another type to females as in Weininger's arrhenoplasm 

 (male producing) and thelyplasm (female producing). Or the 

 differences of sex according to ]\Iinot (18S2) and Schaudinn (1604) 

 are due to specific types of chromatin both of which are present 

 in all individuals derived from a fertilized cell, but male chromatin 

 predominating in males, female chromatin in females. Still others 



