POLYMORPHISM AND LIFE-CYCLES 171 



an inherent property of all living beings, as maintained by many 

 high authorities. 



Whatever view be held with regard to the existence or non- 

 existence of inherent, intrinsic sexual differences in living organisms, 

 it seems clear that the apparent sexual differentiation of the gametes 

 is largely, perhaps purely, adaptive, and furnishes good examples 

 of the principle of morphological differentiation of structure in 

 relation to physiological division of labour. One gamete, termed 

 " female," tends to be bulky and inert, storing up reserve- material 

 in greater or less quantity, a provision (sit venia verbo /) for future 

 requirements ; it is economical of substance, and but few are 

 produced. The other gamete, termed " male," develops in the 

 opposite direction in every respect ; it tends to be small and active, 

 not weighted with superfluous material of any kind, but with motor 

 mechanisms strongly developed ; it is prodigal of substance, and 

 many are produced, but few are favoured by destiny. In extreme 

 cases the female gamete is a relatively huge, inert cell, incapable 

 of movement, crammed with foodstuffs ; the male is excessively 

 minute, and is practically nothing but a nucleus which has its 

 constituent parts packed into the smallest possible space, and with 

 motor mechanisms attached to it. 



In reviewing the progressive differentiation of the gametes in 

 Protozoa, it is convenient to treat separately those forms in which 

 there is little or no ontogenetic differentiation from those in which 

 there is a more or less pronounced difference between the young 

 and adult forms. An example of the first type is seen in Copromonas 

 (Fig. Ill), in which the gametes are ordinary individuals of the 

 species, only differing in that their nuclei have undergone a process 

 of reduction. Good examples of monomorphic forms are furnished 

 also by the Infusoria, a group in which a species may be free-swim- 

 ming, or may be more or less permanently attached and sessile in 

 habit. 



In the free-swimming ciliate Infusoria, sexual differences in the 

 conjugants are frequently not discernible ; if they exist, they can 

 only be inferred from the fact that syngamy takes place, or from 

 subsequent behaviour of the individuals after conjugation, as, for 

 instance, the fact observed by Calkins, that in Paramecium one ex- 

 conjugant multiplies much more rapidly than the other. In other 

 cases differences of size more or less pronounced are exhibited by 

 the conjugants (Doflein, 111). As pointed out above, differences 

 of structure have also been noted in some cases between the 

 stationary and migratory pronuclei produced by a conjugant. 

 Collin (50), however, was unable to find the slightest morphological 

 differentiation of the conjugating pronuclei of Anoplophrya. 



In the sedentary Infusoria, sexual differentiation may be as little 



