70 MARCUS M. HARTOG. 
superfluities—all but indispensable to those that can obtain 
them, not missed by those that have never known them, and 
capable of being laid aside in time by a few of the former class. 
Conversely, referring karyogamic rejuvenescence to mere con- 
stitutional invigoration, we can see that agamy and apogamy 
are harmless conditions where other modes of rejuvenescence 
prevail.? 
C. ALLOGAMY AND SEx. 
Again, if the invigorating effects of karyogamy be due to 
the mere infusion of new blood into the firm ‘“‘ Cytoplast, 
Nucleus, and Co.,”’ it is, of course, an advantage that the new 
blood should be as new as possible within the limits of possible 
harmonious co-operation—that is, usually, within the bounds of 
the race or species. And this must have been the cause which 
determined exogamy in the lowest organisms. In this case 
the members of a brood of gametes are incapable of entering 
into fertile karyogamic union with one another, being affected, 
as we may say, by the disqualification of consanguinity. This 
disqualification has been attributed to a latent sexual differen- 
tiation ; but to admit this view is, as we shall see at once, to 
deprive the word “sex” of the connotation of a differentiation 
of organisms into two complementary categories. 
For if exogamy implied any sexual differentiation in the 
ordinary sense, and we considered any twenty-six broods of 
gametes, say of Botrydium, they should fall into two cate- 
gories, which we will term A—M, N—Z respectively; any of 
the gametes of the former category would be incapable of 
forming fertile union with any other of its own category, but 
would pair freely with any of the other, and vice versa. But 
1 It is interesting to note that Ferns, which are dimorphic, have a resting 
state (spore) interposed between the terrestrial Fern-plant and the palustrine 
prothallus, a sexual karyogamic union between the palustrine and the terrestrial 
states. In some exceptional cases the one or other transitional form of rejuven- 
escence is omitted: in apospory the palustrine form supervenes without the 
resting state of spores ; and in apogamy the terrestrial state supervenes with- 
out karyogamic rejuvenescence : but a combination of these two phenomena is 
not known in the same species, or I think I may say the same group. 
