REPORT ON THE STOMATOPODA. 15 



general rule, in the animal kingdom, that the larvfe 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 tliis 

 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 diflferences between 

 diflfereut genera of larvae are often greater than those between the genera of adults. The 

 fully growTi larva) 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 I'ctainiug 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 the}'' 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 larva) 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, 



