80 Part IT. —Twenty-third Annual Report 
in some measure, be due to the environment ; the conditions, favourable 
and unfavourable, of their life in the Laboratory may have resulted in 
stimulating these irregular forms. The lobsters were under the influence 
of this environment for a month or so while in the egg, and afterwards 
during the whole of their free existence. The parent lobsters were from 
two widely separated localities, viz. the East and West Coasts of Scotland. 
The young forms were mixed together in the hatchery. The different 
origins of the parents might be accompanied by variation in development 
of the larve. 
It is convenient to discuss the stages in the order of their sequence. 
Sracr I,—Saville Kent breaks up this stage into two stages, which he 
separated by two characters :— 
(1) Difference in size. 
(2) Difference in the number of dorsal spines on the carapace. 
Difference in size is not a character of value; and as regards the 
second, I have not been able to discover this difference. 
A very marked difference was found, however, between certain of the 
first zoée, in the shape of the hind border of the telson. | In the majority 
the hind margin makes with the hooks at the angles of the base a return 
curve of comparatively small radius (fig. 30). In some of the larger speci- 
mens Ia. (fig. 67) the telson is broader, the curve of the hind margin is a 
much shallower one, the lateral hooks being directed posteriorly instead 
of inwards (fig. 46). The setae on the hind border are very short, while 
in the first described case the sete were fully half the length of the 
median spine. Now, in Crangon vulgaris,* the second stage ditlers from 
the first in having a telson of slightly different shape, accompanied by a 
greater number of spines on the hind border. There is also a difference in 
size, This fact would suggest the possibility of the two forms in Stage I. 
being independent stages, but the length of the sete was found to be 
variable, and cases occurred where it was impossible to say, from the 
length of the setee, to which form the individual belonged. I have come 
to the conclusion that there is not sufficient differentiation to warrant its 
elevation to a separate stage. 
The second zoea (fig. 68, pl. iv.) is the first stage in which the pleopods 
project. They are unjointed bifid processes. They issue, by foramina 
in the integument, from the posterior part of the under-surface of the 
nd, 3rd, 4th, and 5th abdominal joints. The telson (fig. 48, pl. ii.) has 
16 little setee on either side of the median spine. On the outside of the 
setee there is a little spine at the base of the lateral hook. The uropods 
are not yet free, but may be traced through the integument of the telson. 
Two zoea of this stage measured 10 and 12mm. respectively—a very con- 
spicuous difference in bulk. 
The third zoea shows a certain amount of variation, and between the 
third zoea and the megalops, and in the megalops, variation is well marked. 
The dimorphism was noticed in respect to two characters especially, viz. 
those which are in process of development in the zoea period, e.g. the 
antenn and the pleopods. 
The third zoea (fig. 69, pl. iv.) is characterised by the possession of 
uropods. The telson, which is square, is toothed along its hind border 
(fig. 35, pl. ii.). There were 18 teeth on either side of the median spine 
in the specimen examined. On one side there was a little setose hair. 
Two or three short plain hairs were found on the dorsal surface of the 
margin. The pleopods (fig. 37) are larger ; each consists of a thick stem, 
bearing two paddle-shaped processes. They are constricted off from the 
stem, but not by movable joints. The paddles are set across the abdomen, 
* Vide Williamson. 
