of the Fishery Board for Scotland 157 
The branchia formula of the adult Carcinus menas is as follows :— 
Podobranchiee. | Arthrobranchive} Pleurobranchize. 
First Maxillipede, - | Epipodite 
Second Maxillipede, -| Epipodite 1 1 
Third Maxillipede, - | Epipodite 1 | 2 
First Pereiopod (chela), st oes | Z 
Second Pereiopod, - dn ie a 1 
Third Pereiopod, - AA as 3 1 
ABDOMEN, ab, TExson, T, PLeopops, pl, Plates xi, and xii. 
I, AspomeN (Figs. 118 and 131). The abdomen consists in the 
I. Zoéa of five joints and the telson. On the hind lateral edge of the 
first joint there is a little tubercle, from the middle of the second joint 
a conical process projects on either side. These processes have 
probably a mechanical function, since in certain positions of the 
abdomen they will abut on the hind border of the carapace. They will 
tend to limit the movement of the abdomen. The hind lateral 
border of each of the second and fifth segments projects backwards 
over the beginning of the succeeding joint, and it is minutely notched. 
On the dorsal hind edge of each of these segments there isa pair of 
short plain hairs. The integument of each joint is a cylinder. 
Pieopops. ‘The pleopods are found in this stage as long, somewhat 
oval bodies composed of large rounded cells; they are situated on the 
under-surface of the abdominal segments (pl, Figs. 118 and 131). 
These bodies are seen on all the five abdominal joints. On the first 
joint the body is hemispherical (Fig. 131). Although in structure 
resembling the rudimentary pleopods in the other joints, it does not 
give rise toa pleopod. Its ultimate condition was not determined. 
The pleopod buds in the I. Zoéa are referred to by Spence Bate as 
follows :—‘‘ Close observation will detect the germs of the future 
pleopoda, upon one or two [abdominal segments], situated laterally and 
inferiorly.’ * 
Tetson. The telson (Figs. 122 and 118) isin the adult the shield of 
the anus ; in the Zoéa it, in addition to protecting the end of the gut, 
performs other functions. It is of the form usually found in 
Brachyurus Zoéa. It is deeply forked: each leg curves gently back- 
wards, and tapers toa delicate point. On the dorsal surface of each 
leg there are three long teeth, of which the proximal is the smallest, 
the distal the largest, and the median in position, intermediate in size 
between the two others. The teeth are smooth On the inside of the 
furca, arranged on either side of the anal angle, are three stout 
spines which are elaborately serrated. Three different sets of 
serrations may be made out on each side of the spine (Fig. 120). The 
proximal third is provided with large teeth, the middle third with 
smaller teeth, and the distal third is lined to within a short distance of 
the sharp tip with minute serrations. The inmost spine of each group 
has also on the inner side three long cilia; sometimes a cilium is found 
on its outer side. The serrations on the two sides of the spines were 
not found to be in focus at the same time; it is therefore probable that 
“Opn Cth. 
