be said that the larvae of the
sea-urchin reach on the third day or earlier (according to species
and temperature) the so-called pluteus stage, in which they possess a
typical skeleton; while neither the larvae of the starfish nor those
of the mollusc form a skeleton at the corresponding stage. It was,
therefore, a matter of some interest to find out whether or not the
larvae produced by the fertilisation of the sea-urchin egg with the
sperm of starfish or mollusc would form the normal and typical pluteus
skeleton. This was invariably the case in the experiments of Godlewski,
Kupelwieser, Hagedoorn, and the writer. These hybrid larvae were
exclusively maternal in character.

It might be argued that in the case of heterogeneous hybridisation the
sperm-nucleus does not fuse with the egg-nucleus, and that, therefore,
the spermatozoon cannot transmit its hereditary substances to the
larvae. But these objections are refuted by Godlewski's experiments,
in which he showed definitely that if the egg of the sea-urchin is
fertilised with the sperm of a crinoid the fusion of the egg-nucleus
and sperm-nucleus takes place in the normal way. It remains for further
experiments to decide what the character of the adult hybrids would be.

(b). ARTIFICIAL PARTHENOGENESIS.

Possibly in no other field of Biology has our ability to control
life-phenomena by outside conditions been proved to such an extent as
in the domain of fertilisation. The reader knows that the eggs of the
overwhelming majority of animals cannot develop unless a spermatozoon
enters them. In this case a living agency is the cause of development
and the problem arises whether it is possible to accomplish the same
result through the application of well-known physico-chemical agencies.
This is, indeed, true, and during the last ten years living larvae
have been produced by chemical agencies from the unfertilised eggs
of sea-urchins, starfish, holothurians and a number of annelids and
molluscs; in fact this holds true in regard to the eggs of practically
all forms of animals with which such experiments have been tried long
enough. In each form the method of procedure is somewhat different and
a long series of experiments is often required before the successful
method is found.

The facts of Artificial Parthenogenesis, as the chemical fertilisation
of the egg is called, have, perhaps, some bearing on the problem of
evolution. If we wish to form a mental image of the proce