136 Part L11.— Twenty-first Annual Report 
III—ON THE LARVAL AND EARLY YOUNG STAGES, AND 
RATE OF GROWTH, OF THE SHORE-CRAB (CARCINUS 
MANAS), Leach. By H. Onas. Wiuuramson, M.A., D.Sc., Marine 
Laboratory, Bay of Nigg, Aberdeen. (Plates Vii. ~xiii.) 
CONTENTS. 
PAGE. 
Introduction, . ; : 136 
The Hatching Period : the Occurrence of the Zoéa, : : 137 
The Larval Stages, 5 9 5 : : ; 139 
The Larval Characters, 5 : ‘ j 140 
Development of the Appendages: — 
Antennule, : ‘ : c 142 
Antenna, 5 ‘ ; 5 : ; 144 
Mandible, 3 : , ; ‘ ‘ 145 
First Maxilla, . ‘ ‘ : : : 145 
Second Maxilla, . : : P : ¥ 146 
Maxillipedes, . ; : ‘ 147 
Third Maxillipede, and Pereiopods, : : ; 150 
Branchie, 2 - ; 155 
Abdomen, Telson, Pleopods, ; : : : 156 
External Sexual Characters, . : : ; 160 
The Eye, . ; : : : : 160 
Carapace, é : : : : , : 161 
Thorax, . ; : . ‘5 : 162 
Sizes of the different Stages, : . ; : : 162 
The Rate of Growth, . : 5 : : , 163 
Literature, ; : . : . , : 174 
Explanation of Plates, . ; : : ; 175 
INTRODUCTION. 
A considerable amount of attention has at various times been devoted 
to the larval stages of Carcinus manas. This crab is one of the 
commonest on the British coasts, and its Zoéa may be easily captured 
near the shore by the tow-net during the spring and summer. 
J. Vaughan Thompson first demonstrated the fact that the Zoéa and 
Megalops were developmental stages in the life-history of the decapod 
Crustacea. In 1828 he described* the larva of Cancer pagurus, the 
eggs of which had hatched under his observation. The larva proved to 
be a Zoéa, ‘‘which presented exactly the appearance of Zoéa taurus, 
with the addition of lateral spines to the corselet.” Later, in 1835, in 
the papert in which he showed that the Megalops is also simply a young 
stage of a crab, he described a Zoéa as that of Careinus menas which 
clearly does not belong to this species. The Zoéa of the latter has no 
lateral spines on the carapace, whereas that figured by Thompson has a 
very prominent lateral spine. This mistake was followed by Claus, 
* J. Vaughan Thompson, ‘‘ Zoological Researches,” vol. i, Pt. I., Cork, 1828. 
[According to Cano, Cavolini was the first to recognise the Zoéa. He described and 
figured the larva of Pachygrapsus marmoratus (‘‘ Morfologia dell’aparecchio sessuale 
feminile ecc. nei Crostacei Decapodi ””"—Mitthel. a. d. Zool. Stat. Neapel, ix. Bd., 
4 Heft, 1890, p. 505.] 
+ J. ‘Vaughan Thompson, ‘‘ The Pouhle Metamorphosis in Decapod Crustacea,” Phil. 
Trans. Roy. Soc., London, 1835, p. 859, 1 pl. 
+ Claus, ‘‘ Zur Kenntniss der Mal: acostrakenlarven,” Wurzburger Naturw. Zettschr ; 
