62 



NOTES ON THE DEVELOPMENT OF 

 CARCINUS MAENAS. 



By OLGA M. JORGEXSEN. 



A number of berried hens of the con"imon shore crab were 

 collected from time to time between November and April, and 

 kept in the Laboratory tanks, and the eggs examined at intervals. 

 Early in December, some recently spa^^^iied eggs were examined. 

 They were orange coloured throughout, and the cells showed as 

 yet no differentiation. On January 30th, the same batch of 

 eggs showed the large black eyes of the embryo to have developed 

 sufficiently to be seen with the naked eye. An exammation of 

 the egg at this stage showed the orange coloured portion to occupy 

 only two-thirds to three-quarters of the sphere. The disposition 

 of the embryo within the egg can be seen clearly at this stage, 

 as the chromatophores characteristic of the Zoeae have been laid 

 down already. Those of the abdomen form a chain running across 

 the middle line of the thoracic region, showing the " tail" to be 

 curled round the body. Unfortunately, it is impossible to give 

 any further account of this batch of eggs, as the crab escaped 

 from the tank. 



Another crab examined on April 26th had eggs apparently 

 almost ready to hatch. It was isolated in a small glass tank, 

 through which compressed air Avas bubbled, and on May 1st a 

 number of larvae were found. These were carried round and 

 round in the current induced by the compressed air, and when 

 removed into a Petri dish some were found to propel themselves 

 fairly actively, whilst others lay on their side, the only movement 

 being a spasmodic jerking of the limbs. 



Two separate batches of larvae were kept in this way in the 

 hope that some might be reared through all the larval stages, 

 and some definite records of the length of each stage arrived 

 at, but when two moults had taken place the laboratory attendant 

 shut off the compressed air, with the result that the larvae sank 

 to the bottom of the jars, and next day most of them were found 

 to be dead, and some were covered with a thick growth of Vorti- 



