78 Part III. — Twenty-third Annual Report 



Branchiae of First Zoea Stage. 



1st Row 



PL 



PL 



PL 



PL 









2nd „ 





Ar. 



Ar. 



Ar. 



Ar. 



Ar* 





3rd „ 





Ar. 



Ar. 



Ar. 



Ar. 



Ar. 





4th „ 





Pel. 



Pd. 



Pd. 



Pd. 



Pd. 



Pd. 







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. f There is a little tooth on the side near the anus. On the 

 hind border of the telson there are 16 (17) little setse on either side of 

 the median spine. In the dorsal view of the abdomen and telson the 

 exact number of seta? is not shown on the hind border of the telson. 



Food 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 zoea 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 zoea stages only. 



The difficulty arises from the fact that during the zoea period the 

 different developing appendages do not proceed pari passu; and while, 

 no doubt, there is normally a correlation between the organs 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. 



f Vide Williamson. The Larval and Early Young Stages of the Shore-Crab (Carcinvs 

 )ncenas), p. 157. 



