242 THE AMERICAN NATURALIST. (VoL. XXXIX. 
life history, which must take place with as much regularity as 
the normal development of any organ. As a matter of fact, 
our knowledge of the structure of sexual elements and the events 
of sexual phenomena is almost wholly morphological and for the 
present at least it seems safer to treat and define sexuality from 
a morphological standpoint. 
Under asexual cell unions and nuclear fusions we shall include 
a number of interesting phenomena which can be arranged in 
three groups: (1) cell fusions which have apparently no sexual ` 
relations; (2) cell fusions which are substitutes for a normal 
ancestral sexual process now suppressed; and (3) extraordinary 
modifications of what may have been originally sexual processes 
but which at present serve some peculiar and special function. 
In the first group will be included the extensive union of 
Swarm spores, or the amoeboid elements derived from such, 
best illustrated in the development of plasmodia ; also such cell 
fusions as are clearly for nutritive purposes, as is the union of 
the sporophytic portion of the cystocarp of the red alge with 
auxiliary cells and probably also the fusion of sporidia in the 
smuts and the conjugation of yeast cells. The second group 
embraces the interesting fusions of the nuclei in teleutospores 
of the smuts and rusts and in the basidium with the previous 
history of the paired (conjugate) nuclei in the mycelium, perhaps 
also the nuclear fusions in the ascus, and such cell unions as 
have been reported preliminary to the apogamous development 
of the fern sporophyte, The third group includes the remarka- 
polar nuclei and the triple fusion of these with the second sperm 
nucleus, frequently called “double fertilization." 
The well known union of the swarm spores of the Myxomy- 
cetes as amceboid cells (myxamæbæ) to form the plasmodium is 
one of the best illustrations of a fusion of protoplasm without 
sexual significance. In this general union of hundreds and per- 
haps thousands of small cells there are no nuclear fusions so far 
as is known, but simply the merging of the cytoplasm to form a 
large multinucleate unit. The whole phenomenon indicates a 
coóperative process which is probably economical of nutritive 
functions in the semiterrestrial conditions under which plas- 
