4 
THE VOYAGE OF H.M.S. CHALLENGER. 
for existence as tlie adults, they have undergone countless secondary modifications which 
have no reference to the life of the adult, and are therefore unrepresented in the adult 
organism ; and a comparison of the various larvae which are here figured and described 
will show that they differ among themselves more than the adults, thus reversing, the 
general rule that larvae are less specialised and exhibit clearer evidence of genetic relation- 
ship than mature animals. The problem which they present is very similar to, but more 
difficult than, that presented by the Hydro-medusae, for young Medusae can be reared 
from the hydroids in aquaria without difficulty, and it is also easy to rear young hydroids 
from the eggs of Medusae, but the life-history of the Stomatopoda must be traced from 
the internal and indirect evidence furnished by comparison. 
The Stomatopod larvae present differences among themselves, and they may be 
arranged in genera and species, but unfortunately their generic characteristics are quite 
different from those upon which the adult genera are based, and this is true in a still 
greater degree of their specific characteristics. As the larvae undergo great changes during 
their growth, different stages have been described as distinct species or even genera, and 
it is not easy to select from the rich gatherings which are brought home by collectors, the 
successive stages in the history of a single species. Like the adults, they are widely dis- 
tributed, and a gap in a series from the North Atlantic may be filled by a specimen from 
the coast of Australia or the Sandwich Islands, and the collection from a single locality 
may contain the larvae of several widely separated species of adults in all stages of 
growth. 
The attempt to unravel the tangled thread of the larval history of the Stomatopoda 
is therefore attended with very exceptional difficulties, and the earlier writers were 
content to rest after the bestowal of generic and specific names upon the larvae, and the 
first writer to approach the subject in a scientific spirit was Claus, whose classical mono- 
graph not only abounds in fundamental generalisations of the greatest interest and value, 
but also contains nearly all that we know regarding the relationship between the larvae 
and their adults ; but the Challenger collections, especially the rich collections of Alima 
larvae, a group in which Claus’s collections were very deficient, furnish the material for 
revision of the subject, and enable us to determine, with much greater certainty than 
before, the larval type which pertains to nearly every one of the genera of adult 
Stomatopoda, and also to give a pretty complete picture of the developmental history of 
each larval type. As the specific differences between the adults are very slight, the 
specific identity of each larva can be determined only by rearing the adult from the 
larvae, but this fact renders it the more important that the series collected by the 
Challenger should be figured and described, as later investigators will thus be enabled to 
complete the history by keeping the final stage in each series alive in an aquarium until 
it assumes the characteristic of the adult. This can be done without difficulty, as the older 
larvae are hardy, while the fact that the younger larvae will not live in captivity 
