80 



We now come to the question concerning the characters of the species. It appears 

 hat everywhere, except within the just mentioned group of Sphcer. Leuckartii, the mahs 

 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, winch do not occur in the other sex. Other distinctive marks are not 

 unfrequently found in the antennulae, the maxillae 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 setae, 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 antennulae, the maxillae and the maxillipeds, 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-covering, 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 Sphceronella, 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 Sphceronella 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 larvae 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 larvae are known 

 to me, and these not only differ from all other larvae yet found, they also show very distinct 

 differences among themselves, particularly in the frontal decoration and in the two distal 



