of the Fishery Board for Scotland. 



11 



with the laboratory. Apart from the cost of the distribution of 

 the fry, the expenditure on the hatching work is now under £100 

 per annum, and the total expenditure does not greatly exceed 

 that sum. 



Besides the hatching of the plaice above referred to, the hatching 

 of lobsters and crabs was also undertaken by Dr. H. C. Williamson 

 at the request of the fishermen on the coast of Aberdeenshire. 

 About 4,500,000 larva3 of the crab, and three thousand young 

 lobsters — most of which were reared through several stages, and in 

 some cases nearly to the stage at which the adult form is assumed — 

 were liberated along the coasts of Aberdeen and Banffshire. In the 

 case of the plaice, it may be explained, the time during which the 

 embryonic and larval fishes are protected extends to about half the 

 period of their pelagic life, at the end of which they settle on the 

 bottom as young flat-fishes. 



Since the hatchery was established the number of the fry of 

 the food fishes which have been produced at it amounts to 

 303,752,000— viz., 286,855,000 plaice, 5,727,000 lemon soles, 

 5,160,000 turbot, 4,010,000 cod, and 2,000,000 of others. Of the 

 plaice, 136,065,000 were produced at Dunbar, when the liatchery 

 was situated there, and 150,790,000 at the Bay of Nigg since 1900. 



The Development of the Ckab. 



The present Report also contains a paper by Dr. H. C. William- 

 son on the larval and early young stages of the common shore 

 crab (Carcinus mmnas), in which the developmental changes that 

 occur are traced with great care and minuteness. It is comple- 

 mentary to another paper on the edible crab contributed by the 

 same naturalist to the Nineteenth Annual Report. The character 

 and structure of the various appendages in the Zoea stages and in 

 the Megalops are fully described and illustrated by a large series 

 of figures, and the features which distinguish these stages from the 

 corresponding stages of other forms are detailed. The development 

 of the branchiae or gills is very fully treated. A number of obser- 

 vations were also made in regard to the reproduction, the rate of 

 growth, and the moulting of the crustacean in question. The 

 duration of the period of incubation of the eggs has not yet been 

 determined, but it probably exceeds four months. 



The period of hatching extends over a considerable number of 

 months — viz., from March to the end of July — and berried 

 females may be got on the beach between tide-marks during nearly 

 the whole year with the eggs of different females in very different 

 stages of development. The eggs are at first straw-coloured, 

 becoming deep-amber as development proceeds, and dirty-grey 

 before hatching. The larval crab leaves the egg in the so-called 

 Protozoea stage, which is transitory, the delicate integument being 

 immediately cast, and it then appears as a Zoea, of which there are 

 four stages, each following a moulting. At this time it is wholly 

 pelagic, or free-swimming, a mode of life which appears to last for 

 about a month or a little less. The next moult gives rise to the 



