AND OTHER BRITISH PRAWNS. 113 



end of the month or in June by the younger females. During 

 June and the first half of July every female taken either bears 

 eggs or can be shown to have hatched young; but about the 

 middle of July, though a large proportion bear eggs, many have 

 evidently ceased to breed. For example, out of 103 specimens 

 taken on July 14 there were 33 with eggs, 46 without eggs, and 

 24 males. In all the females the ovary was empty. 



Egg-bearing females migrate down into salt water as the time 

 of batching approaches, and, so far as my observations go, the 

 larvae are very rarely hatched in the river itself. While I have 

 had the larvae hatch in aquaria in salt water on several occasions, 

 they have never done so when the parent has been kept in fresh 

 or slightly brackish water. In such cases the eggs are eventually 

 stripped off. In more than one case a female kept in fresh water 

 past the time at which the young were expected to hatch has 

 been put directly into salt water, with the result that the young 

 have ha.tched during the following night. Probably hatching 

 takes place always at night under normal conditions, and the 

 young are carried out to sea by the ebb-tide. I have only once 

 caught a single larva in an early stage of development, in spite of 

 much search in Breydon Water at the height of the breeding- 

 season. A few larvae in the last stage are occasionally found in 

 Breydon, and doubtless metamorphose there, but the great 

 majority must complete their development at sea and migrate up 

 the rivers in the post-larval condition. Young prawns have been 

 taken 12 miles up the river towards the end of August between 

 19 and 25 mm. long, but it is by no means easy to obtain these 

 young stages, and it is probable that they are to be found in 

 Breydon much earlier. On the other hand, a very careful search 

 for them on August 28, 1922, in the shallows and among 

 Zoetera, was entirely unsuccessful, so that it is not improbable 

 th'c. 'j immigration is delayed to a later stage than is the case in 

 L. squilla. Mortenseu found that the yovmg of L. adspersus, 

 though appearing in the shallows about the middle of July, do 

 not reach the innermost parts of certain fjords during the first 

 summer. 



Moulting. 



The process of moulting takes place usually at night, but I 

 have been fortunate in having been able to witness it on two 

 occasions during the daytime. On each occasion the prawn was 

 found in a peculiar position, the body greatly flexed, the head 

 bent sharply downwards. The cuticle breaks between the thorax 

 and abdomen, leaving the anterior sclerite of the latter attached 

 to the first segment. The thorax then bulges out through the 

 opening, and the animal draws the whole of tlie thorax and 

 appendages out evenly, without pause. Immediately after freeing 

 the eyes and antennae, the animal gives a sudden leap forwards, 

 freeing the abdomen instantaneously. The whole process took a 



Proc, Zoot. Soc— 1923, No, VIII, 8 



