REPORT 03ST THE STOMATOPODA. 
15 
general rule, in the animal kingdom, that the larvae or young of related species are less 
divergent than the mature animals. Even if we were able to rear the larvae of the Stomato- 
pods, and thus to use the evidence which they supply, this rule would not apply in this 
case. The larval life is so long, and forms such a considerable part of the total life of 
each individual, and the larvae are so perfectly developed, and their relations to their 
environment so complex, that there are about as many species of larva as of adults, and the 
specific differences between them are fully as pronounced ; while the differences between 
different genera of larvae are often greater than those between the genera of adults. The 
fully grown larvae are in no sense embryonic or generalised ; they have no reproductive 
organs, but in all other particulars they are just as highly organised as the mature 
animals, and if the animals were to become sexually mature while retaining the organisa- 
tion which fits them for their pelagic life, and if the final sedentary stage were then 
dropped, we should then have an order of pelagic Crustacea of as high organisation, and 
with as many well-defined genera and species, as the order Stomatopoda. 
The larvae may thus be treated exactly as if they were adults, and a natural or 
phylogenetic classification of them established by the comparative study of their 
organisation exactly as we have done for the adults. 
As each larva is only an immature adult, or each adult only a fully grown larva, the 
genetic history of each specific adult must be identical with that of some specific larva, 
namely, its own larva. 
If, then, comparative anatomy enables us to trace from the study of the adults of an 
order or family or genus, their natural or genealogical classification, it must of course be 
possible to do the same thing with the larvae, and if the classification which is established 
is natural, there must be a discoverable relation between the one derived from the larvae 
and the one derived from the adults. 
In most cases this is unnecessary, as we are able to trace the young to its 
adult form, and to use the whole life history as a basis for classification, and in most 
cases it would also be extremely difficult, on account of the embryonic or generalized 
character of young animals, and the absence of conspicuous specific differences, but it 
fortunately happens that in the Stomatopoda, where we are compelled to resort to 
this or some other indirect method for discovering what larva pertains to what adult, it 
is also much more easy than usual, owing to the high specialisation and great diversity 
of the larvae. 
We cannot expect absolute agreement between the two classifications, for the sources 
of our evidence can never be complete. We knew nothing of the larval types which may 
have existed in the past, and next to nothing of the fossil adults, and it is very probable 
that some of the larvae belong to unknown adults, and also that the larvae of some of 
the known adults are as yet undiscovered, and it is very probable that two allied adults 
may have remained alike, while their larvae have been modified in two divergent directions, 
