192 TRANSACTIONS LIVERPOOL BIOLOGICAL SOCIETY. 



formerly regarded as a distinct species (A. rosea of Rathke, 

 A. nexa of Thompson). Garstang,* however, showed that 

 they were the young stage of A. punctata, and that when kept 

 in a tank and fed on different weed they changed colour and 

 became first brown and finally olive green, the inference being 

 that these colour changes represent the protective colouration 

 exhibited by the animal as it passes through the Laminaria 

 and Fucus zones respectively, during its migration from deep 

 water to its breeding grounds, as it becomes mature. 



After the period of oviposition in the spring it is not 

 known what happens to Aplysia. Mediterranean fishermen 

 assert that it becomes full grown in one season, lays its eggs, 

 and dies. Confirmation of this statement is indicated by 

 observations made at the Plymouth Laboratory. Dr. Orton 

 thinks that Aplysia is probably an annual, and that it attains 

 the length of 6-8 inches in a single season. Dr. Orton's records 

 also point to an early and a late brood of young, the first 

 reaching the red stage about July, and the second about 

 September at Plymouth. Thus the wintering forms spawn in 

 the spring, and the young produced may reach maturity and 

 spawn in the autumn. It is also possible that the same 

 individual can produce two broods during its life-time. 



There are, therefore, the following stages in the life- 

 history : — 



1. Pelagic veliger (larval) stage hatching from shore-laid 



e gg s - 



2. Metamorphosis (unknown). 



3. Rose-red stage in red alga zone on sea bottom. 



4. Brown stage in Laminaria zone. 



5. Olive green stage in Fucus zone. This is the mature 

 stage when spawn is produced. 



6. If the individual survives egg-laying it may return 

 to deeper water. 



* Garstang. " Journ. Mar. Biol. Assoc." 1889-1890. 



