78 Part I[I.—Twenty-third Annual Report 
Branchic of First Zoéa Stage. 
lst Row - Pi. ge Pl, Pl. 
2nd ,, - ie Ay. Ar, Ar. AY.) yAr™ 
Ord 45 - ce Ar, Ar, Ay. Ar. Ar. 
Ath ,, - a Pd. Pd; Pd...) Gd.) eee Pd. 
aia - Ep Ep Ep. | Ep Ep Ep 
Appendage. | 5 per. | 4 per. | 3 per. | 2 per.| 1 per.| 3 mp. | 2 mp. 
ABDOMEN. 
On the dorsum of the abdomen there are three single spines and a pair 
of hooks. The spines arise from the third, fourth, and fifth abdominal 
segments, and the pair of hooks are situated on the hind border of the 
sixth segment. In the larva of the American lobster there is a small 
hook on the second segment also. 
There are four pairs of rudiments of pleopods; they are paired 
swellings projecting below the ventral line. Each is widely separated 
from the other pleopod of the pair. The integument is apparently per- 
forated for the outward growth of the appendage, in a manner similar to 
the bud of a new limb, Inside, a fold can be seen. 
In each segment there is a pair of nerve ganglia. In the examination 
of the first stage of Carcinus the ganglia are noticed, but were not 
recognised.t There is a little tooth on the side near the anus. On the 
hind border of the telson there are 16 (17) little sete on either side of 
the median spine. In the dorsal view of the abdomen and telson the 
exact number of sete is not shown on the hind border of the telson. 
Foop oF THE ZOEA. 
he stomach of one zoea contained the integument of a copepod. 
SUBSEQUENT STAGES. 
As mentioned above, there has been some difference in opinion regard- 
ing the number of stages into which the zoéa period is normally divided. 
In the European lobster Sars distinguished three stages; Saville Kent 
made out four distinct stages ; Chadwick has described three stages, 
Herrick, for the American lobster, discriminated three zoéa stages only. 
The difficulty arises from the fact that during the zoéa period the 
different developing appendages do not proceed part passu; and while, 
no doubt, there is normally a correlation between the crgans which results 
in a certain stage of development in the one being usually associated 
with another certain stage in the second appendage, still the variation 
*The arthrobranch in the second row, connected with the third maxillipede, 
is hidden by the adjacent arthrobranch of the first pereiopod. 
+ Vide Williamson, The Larval and Early Young Stages of the Shore-Crab (Carcinus 
menas), p. 157. 
OTe 
-f 
