BIOLOGICAL ANALOGiEg. 
parent, and finally from the amoeboid form results the perfect imago, 
or image of the plant from which originally the ovum was derived. If 
exception should be taken to any of the Myxogasters being employed 
in illustration, inasmuch as their vegetable nature has been called in 
question, then we can fall back on the life history of Volvox globator, 
Stephanos 2 )hcera, and other of the Volvocinece, to say nothing of mosses 
and Characece, already alluded to, which furnish less perfect trans¬ 
formations. Although not conducted on so large a scale as in the 
animal kingdom, it is clear that we have at least suggestions of meta¬ 
morphosis also in the vegetable world. 
Alternation of generations, as applied zoologically, differs 
materially from metamorphosis, although they are sometimes con¬ 
founded as though they were convertible terms. The fundamental 
idea is that of an organism “ producing an offspring which at no time 
resembles its parent, but which, on the other hand, itself brings forth 
a progeny which returns, in its form and nature, to the parent animal, 
so that the material organism does not meet with its resemblance in 
its own brood, but in the descendants of the second, third, or fourth 
degree or generation, and this always takes place in the different 
animals which exhibit the phenomenon in a determinate generation, 
or with the intervention of a determinate number of generations.” 
The characteristic difference between this and a simple metamorphosis 
is that each generation completes its career in the same form as it 
commenced, so that each starts from an ovum, and the cycle is not the 
career of a single individual, but of a consecutive series of individuals, 
which revert to the original form after one, two, or more intermediate 
and differing generations. 
In Ferns an alternation of generations is evident. The fronds of 
mature ferns bear on their under surface, or margin, clusters of spore- 
cases containing minute spores, which themselves are produced without 
sexual fertilisation. These spores germinate and produce a little plant 
called a prothallium, not at all like the parent fern, but a small simple 
plant nourished by root-hairs. This prothallium is capable of repeating 
itself by buds, but finally it produces male and female organs, and 
the result of fertilisation is a true embryo, sexually produced, which 
develops into a Fern, like its asexual parent. Thus there is an 
alternate asexual and sexual generation, the sexual being the small 
prothallium, and the asexual that more imposing form which we are 
in the habit of calling a Fern. 
In Mosses a somewhat similar alternation prevails. The ger¬ 
minating spore produces a confervoid thallus called a Frotnnemci; from 
this the leafy moss is developed by buds on the branches. Sexual 
organs are formed, and finally, after fertilisation, spores are produced. 
It is unnecessary to repeat instances, since my object is more 
suggestive than exhaustive, and in fact the subject could not possibly 
be extended in all its details within the narrow limit of time at my 
disposal. 
