BIOLOGICAL ANALOGIES 
^51 
BIOLOGICAL ANALOGIES * 
BY M. C. COOKE, 
M.A., LL.D., A.L.S., ETC. 
The phenomena of reproduction in animals and plants present 
many features worthy of comparison. It is scarcely rash to say that 
sexuality is as common and universal in the vegetable as in the animal 
kingdom. Not many years ago such an assertion could scarcely have 
been ventured upon with confidence, when the reproduction of the 
lower cryptogamia was so little known, but every new discovery adds 
strength to a belief in universal sexuality. The completeness of the 
sexual organs and their functions is not a matter of mere speculation. 
The male and female organs are definite and distinct. They approach 
each other, as it were, instinctively, and unite. The ovary receives 
the contents of the antheridium, which, in many cases, are multi¬ 
tudinous active spermatozoa, with a remarkable similarity to the 
same bodies high up in the zoological scale. The opening of the ovary 
just as the spermatozoids are matured, as in the genera LEdogonium 
and Vauclieria, the entrance of these and their absorption, and finally 
the maturing of the fertilised ovum, are notable analogies. If we seek 
more special and particular examples these can be found. What, for 
instance, could be more suggestive of the fusion which takes place in 
some of the Infusoria, in which two individuals meet, collide, and 
finally coalesce in one individual, than the conjugating zoospores in 
Botrydium gramdatum, where two active zoospores unite, and by their 
union become a true fertilised isospore, in which all motion soon 
comes to an end, and is followed by the development of a young plant 
like its original parent. These are some of the phenomena which 
startled certain of our progenitors into the supposition that infusoria 
were generated within, and ultimately escaped from, the tissues of 
living plants. 
Metamorphosis, such as we are acquainted with in insects, has also 
its analogue in the vegetable kingdom. From the egg of a butterfly 
emerges, not a form like the parent, but a caterpillar, which passes 
through a period of existence and then comes to rest; it changes into 
a pupa or resting condition, in which it remains for a more or less 
lengthened period, then its final change takes place, and the perfect 
imago appears, the true image of the original parent. In some of the 
lower plants we may recognise a similar metamorphosis. In some of 
the Myxogasters, for instance, the spore, which is the ovum or egg, 
produces a larval form, an active zoospore. After a time this becomes 
amoeboid, more sluggish, and quite different from either zoospore or 
* This extract is taken from a most interesting address delivered by Dr. 
Cooke, President of the Quekett Microscopical Club, at the Annual Meeting, 
held July 27th, 188.3. 
