80 Part III. — 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 larvae. 



It is convenient to discuss the stages in the order of their sequence. 

 Stage 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 zoeae, 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 la. (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 seta3 on the hind border are very short, while 

 in the first described case the setae were fully half the length of the 

 median spine. Now, in Crangon vulgaris* the second stage differs 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 setae was found to be 

 variable, and cases occurred where it was impossible to say, from the 

 length of the setae, 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, pi. 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 

 2nd, 3rd, 4th, and 5th abdominal joints. The telson (fig. 48, pi. ii.) has 

 16 little setae on either side of the median spine. On the outside of the 

 setae 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 

 antennae and the pleopods. 



The third zoea (fig. 69, pi, iv.) is characterised by the possession of 

 uropods. The telson, which is square, is toothed along its hind border 

 (fig. 35, pi. ii.). There were 18 teeth on either side of the median spine 

 in the specimen examined. On one side there w r as 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. 



