942 DR. H. J. HANSEN ON CRUSTACEANS [ Dee. 1, 
yellowish eyes, which possessed a shape recalling somewhat the 
very curious, ovate, and obliquely implanted, but much larger eyes 
in S. ancylops, Kr. The result of further comparison was that 
every conceivable intermediate stage between the small 8. ancylops, Kr. 
(with its abnormal eyes, its rudimentary last pair of trunk-legs, 
and its dorsal spines on some of the abdominal segments, &c.), 
and large, mature specimens of 8. atlanticus, M.-Edw, (8. frisii, Kr.), 
was found. We possess S. ancylops from 17 localities, and 
in 10 of these it was taken in company with larger transition- 
stages to, or completely developed specimens of, S. atlanticus. 
That typical specimens of S. ancylops and transition-stages 
to the black-eyed form do not possess any petasma, scarcely 
needs mention, but neither was it found in the smallest of the 
black-eyed specimens. The result was that S. ancylops, Kr., must 
be considered as the Mastigopus-stage of S. atlanticus, M.-Edw., 
and that the idea of Mastigopus must be extended to embrace such 
stages as only differ from the Mastigopus of Claus, Bate, and 
Ortmann in having the fourth and fifth pairs of trunk-legs some- 
what longer, while their eyes in shape and colour have still 
preserved the essential characters of the Mastigopus. And with 
that I had gained a result rendering it easy to study the alterations in 
shape and armature of all the various parts of the animal during its 
development, and a starting-point for the consideration of other 
species. Soon afterwards | made out that S. rinkii, Kr., is the 
Mastigopus of S. arcticus, Kr., &e. And now let us look at the 
characters of the larve in contradistinction to those of the adult 
animals. 
When a species is mature the male sex always possess a large 
petasma and—so far as we know—a peculiar development of the 
exterior flagellum of the antennule. For the females I have not 
found any character of discriminative value. But while the well- 
developed petasma is necessary to decide the real maturity of 
the male, and the female must have reached the same length as the 
adult male before it can be admitted as being mature, such 
comparison is not necessary for the decision of the question whether a 
specimen without a petasma has arrived at the adult stage—viz. that 
its different parts, such as shield with rostrum, eyes, external maxu- 
lipeds and legs, uropods, telson, Sc. have almost or totally assumed 
the shape to be found in the mature and sometimes unknown form—or 
whether it must be considered as a larva. As declared in the 
introductory remarks, about two-thirds of the established species 
are but larve; in reality they present several characters immediately 
stamping them as such, and, furthermore, they show peculiarities 
which indicate very different stages of metamorphosis. In a 
multitude of “ species” dorsal spines on some or almost all the 
abdominal segments are present, and such spines only exist in the 
larval stages, but in many older larve the abdomen is quite smooth. 
In the adults the rostrum is rather short or very short, but, 
especially in the younger Mastigopus-forms, it is most frequently 
long or even very long. In the larve the fourth and fifth pair of 
