80 
We now come to the question concerning the characters of the species. It appears 
hat everywhere, except within the just mentioned group of Spher. Leuckartii, the males 
offer a considerable number of excellent and, as a rule, easily observed characters. In this 
respect they generally surpass the females; they are not only easier to examine, but the 
shape and decoration of the frontal margin, the processes from the sub-median skeleton, their 
often very peculiar two pairs of trunk-legs and the hair-coat of their trunk frequently afford 
excellent characters, which do not occur in the other sex. Other distinctive marks are not 
unfrequently found in the antennule, the maxille and the maxillipeds, in the presence or in 
the want of caudal stylets, and in the former case, often in the length of their longest 
terminal seta etc. But, at the same time, we must point out that minor differences in the 
general shape of the body, in the distance of the caudal stylets from the posterior extremity, 
in the length of very long sete, are frequently seen in specimens of the same species; also, 
that such a feature as the rostrum protruding or receding may give a very different appear- 
ance to the animal. In the females the chief characteristics are found in the structure and 
the organs of the head, especially the antennule, the maxilla and the mavxillipeds, and in 
adult specimens usually in the genital area, (in Mysidion, however, in the arch round each 
genital aperture). As a rule the heads of the females are much more uniform than those of 
the males, and must be examined with great care; the size of the genital area compared with 
that of the head, its form, the extent of the solid chitine, as well as its hair-covering or want of 
hair-coyering, often afford good characters; nevertheless, it is often necessary to make a prepara- 
tion, and as far as my experience goes, one must frequently pass over several smaller differences, 
as some variation may be found in the same species. The caudal stylets, their position etc., or 
the want of them, is always of importance. Within the genus Spheronella, the females of 
many species have trunk-legs, whereas these appendages are wanting in others, but in adult 
specimens they are often so hard to find, that the character drawn from their presence is 
not easy to make use of, and one has to examine the animals very carefully before being 
able to deny their existence. In the adult females of very few species we notice a peculiar 
haircoat, but it must be remembered that in Choniostoma Hansenii the younger specimens 
are more hairy than the adults, and e. g. in Spheronella danica, the trunk of the young 
ones is closely covered all over with hair, that of the adults mostly or totally naked. In 
the females the general shape of the body is sometimes rather characteristic, but often 
rather variable according to chance circumstances, e. g. some kind of pressure, or the periods 
of beginning and ceasing to lay eggs. 
But, in order to find good characters of the species, we are not confined to the 
males and females only. In a large material it is not difficult to procure larve of a number 
of species, partly free specimens, partly in preparing those contained in one or some of the 
ovisacs. Of all the five species found in the marsupium of Cumacea, the larve are known 
to me, and these not only differ from all other larve yet found, they also show very distinct 
differences among themselves, particularly in the frontal decoration and in the two distal 
