of the Fishery Board for Scotland. 



137 



Thompson gave drawings of what he labelled the Megalops and first 

 young form of Carcinus. He believed that they were derived from the 

 Zoea just mentioned. The Megalops and first young stage do belong to 

 Carcinus mceitas, but they were not derived from the Zoea in question. 



R. Q. Couch in 1843 described* the Zoea of Carcinus, which he 

 obtained by keeping the berried female in captivity until the eggs were 

 hatched. He gave drawings of the Zoea, Megalops, and first young 

 stage of this form ; the sketches of the two former are not diagnostic. 

 Both Thompson and Couch regarded the Zoea stages as one stage, and 

 the Megalops as the second stage. While they recognised that the Zoea 

 grew larger, and that certain organs developed during the Zoea period, 

 they did not state distinctly that these changes in size, etc., are brought 

 about by moults, not merely by gradual growth. Thompson also 

 discriminated between young and full-grown Megalopa. 



Du Canet had in 1839 given a description with drawings of the 

 Protozoea and first Zoea. 



The first exhaustive treatment of the Zoea and Megalops stages was 

 made by Spence BateJ in 1859. In tracing the development of the 

 Zoea he drew attention to the fact that the changes from a Zoea to the 

 crab are gradual and not really of the nature of a metamorphosis. 

 He said in this connection (jo. 590) — "In the highest types of Crustacea, 

 the immense variety of change from the Zoea to the complete animal is 

 but the result of subordinate becoming more important parts, together with 

 the development of others not yet present, and therefore hardly accept- 

 able under the signification of metamorphosis." "The author is 

 perfectly aware that in Insecta the change of the animal within the 

 chrysalis is gradual in development ; but he wishes to show that there 

 is no stage in Crustacea answering to the chrysalis ; that the moults in 

 process of development of the Crustacea are of the same kind as those 

 which take place in the adult condition." 



Spence Bate gave drawings of the appendages, and traces their 

 development through a number of stages. They are, however, made on 

 a small scale, and are to a considerable extent vitiated by the fact that 

 stages belonging to species other than Carcinus have been introduced 

 into the series. He depicted three Zoea stages, of which the last does 

 not belong to Carcinus. He did not satisfy himself as to the number of 

 moults which take place in the Zoea period, and he was of the opinion 

 that the Megalops stage was a period of stages analogous to that of 

 the Zoea period. He had arranged two Megalopa and a young form 

 into a series. The first of these is not a Carcinus, the second and the third 

 could not from the drawings be recognised as belonging to this species. 

 There is only one Megalops stage. 



Brooke described the Megalops and six successive stages of Carcinus, 

 He, following Spence Bate, regarded the Megalopa which he had collected 

 as belonging to the last Megalops stage. His drawing of the Megalops 

 does not show the characteristic long curved bristles which are present 

 on the dactylopodite of the fifth pereiopod of this stage. 



The Hatching Period: the Occurrence of the ZoM. 



No investigation was made with the view of finding out during how 

 many months the Zoese of Carcinus were to be found in the sea, but 



* R. Q. Couch, "On the Metamorphosis of the Decapod Crustaceans," Eleventh Annual 

 Report of the Royal Cornwall Polytechnic Society, Falmouth, 1843 ; 1 pi. 



f Du Cane, "On the Metamorphosis of the Crustacea," J Mjeti/i- of Natural History. 

 vol. iii., 1839 ; 1 pi. 



X Spence Bate, "On the Development of Decapod Crustacea," FML Trans. Roy. Soc, 

 London^ 1859, p. 589, pi. xl.-xlvi. 



