ALTERNATION OF GENERATIONS. 653 
of which lay eggs, while the redia or proscolex of the same 
worm produces cercarie by internal budding. Here also 
may be cited the cases of strobilation of the Aurelia, the 
tape-worm, the Nais, Syllis, and Autolycus, among Anne- 
lids. Thusamong Ceelenterates and worms, as well as some 
Crustacea, a large number of individuals are produced, 
not from eggs, but by budding. 
Similar occurrences take place among insects, as the 
Aphis or plant-louse, in which a virgin Aphis may bring 
forth in one season nine or ten generations of Aphides, so 
that one Aphis may become the parent of millions of 
young. These young directly develop from eggs or buds 
which are never fertilized, hence the term parthenogenesis, 
or virgin-reproduction, sometimes called agamogenesis (or 
birth without marriage). The bark-lice as well as the 
Aphides develop in this manner during the warm wea- 
ther ; but at the approach of cold both male and female 
Aphides and Coccide appear, the females laying fertilized 
eggs, the first spring brood thus being produced in the 
normal, usual manner. 
Still more like the production of young in the redia of 
the Trematode worms is the case of the larva of a small gall- 
gnat (Miastor), which during the colder part of the year from 
autumn to spring produces a series of successive generations 
of larve like itself, until in June the last brood develops 
into sexually mature flies, which lay fertilized eggs. 
While the larval Miaster produces young like itself, the 
pupa of another fly, Chironomus, also lays unfertilized eggs. 
A number of moths, including the silk-worm moth, are 
known to lay unfertilized eggs which produce caterpillars. 
Among the Hymenoptera, the currant saw-fly, certain gall- 
flies, several species of ants, wasps (Polistes), and the honey- 
bee, are known to produce fertile young from unfertilized 
eggs; in the case of the ants and bees, the workers lay eggs 
which result in the production of males, while the fertilized 
eggs laid by the female ant or queen bee produce females 
or workers. 
Taking all these cases together, parthenogenesis is seen to 
be due to budding, or cell-division, or multiplication. Now, 
