of the Fishery Board jor Scotland. 



171 



Among specimens less than a year old, found at any date, a large 

 amount of variation in size will be found. This is in part due to the 

 fact that the young of Carcinus are hatched during a period of several 

 months. It therefore happens that in the autumn some have gained a 

 considerable size, e.g. ^ inch, while others may not exceed ^ inch. The 

 hatching period, as stated above, lasts from March till at least the end 

 of July. 



The Megalops stage has been selected as a convenient period from 

 which to calculate the age of the crab. Three of the crabs, viz. Nos. 

 19, 20, and 21, Table III., were reared from the Megalops. No. 7 was 

 probably in the first young stage when it was found, and Nos. 10 and 

 11 (2*5 mm.) have been regarded as belonging to the second young stage, 

 i.e. one cast has intervened between it and the Megalops. Nos. 2, 3, and 4 

 had probably already passed through six moults when captured. They 

 measured respectively 6, 6-25, and 6-5 mm. I have assumed that the three 

 last had been in the Megalops stage in March, and that No. 7 was at a 

 similar stage in April, and Nos. 10, and 11 in May. No. 16 (3 mm.) is 

 in the third stage, and is supposed to have been a Megalops in June. 



In this Table the attempt has been made to arrange together crabs 

 that were probably hatched out in the same month. For this purpose 

 five different groups have been recognised among the crabs that compose 

 the series. In the case of the crabs which were very small when cap- 

 tured the month in which they were in the Megalops stage may be fixed 

 for all practical purposes with certainty. These crabs of known age then 

 form the standard by which the ages of larger crabs are judged. 



In the first group are included those crabs which were in the Megalops 

 stage very probably in March. Group II. contains certain crabs 

 which were in the Megalops in April, and Group III., in May. The 

 supposed June crabs appear in IV., while in V. are included four, the 

 ages of which are known. 



Crabs Nos. 5 and 6 are admitted into the first group ; they measured 

 12 '5 and 12 mm. respectively in September, and are evidently the young 

 of the hatching season just ended. The age of these crabs may then 

 with reason be estimated on the date of capture to be only a few 

 months. 



The number of casts that the young crab passed through in its first 

 year varied. Thus No. 21 cast 8 times in its first twelve months ; No. 20, 

 however, cast 1 1 times in its first seven months ; while No. 1 9 cast only 6 

 times in the first seven months. No. 7 had moulted 1 3 times at least in its 

 first year, while Nos. 10 and 11 had passed through 9 (?10) ecdyses in 

 the same time. Regarding Nos. 2, 3, and 4 as being when captured in 

 their sixth young stage, we have at the end of the year (end of February) 

 11, 11, and 10 casts respectively. 



The five groups are divided by horizontal lines into 1-year periods, the 

 year being calculated from the Megalops stage. 



Great variation is found in the size of the crab when one year old 

 No. 21 at the end of the first twelve months measured 11'6 mm. ; No. 

 7 measured 22 mm., and Nos. 10 and 11, 8 and 12*75 mm. respectively. 

 Assuming that Nos. 2, 3, and 4 were in the Megalops stage in March, 

 which is the earliest in the year that we are justified from our knowledge 

 of the hatching season in fixing, they cannot at the end of February be 

 more than one year old. They then measured respectively 19, 19*5, and 

 21 mm. in breadth. The most marked difference is, however, seen in 

 Nos. 19, 20, and 21. The first and last are Brook's specimens. No. 20 is 

 one of Waddington's series. The latter in seven months reached a breadth 

 of 18 mm., while the former were at the end of the same period 5*1 and 

 5*2 mm. respectively. The crabs were not exposed to identical condi- 



