Occurrence of Two Generations of Nudibranchs. 13 
of large size, the former averaging 26 mm. by 17 mm., the latter 17 mm. by 
85 mm. The specimens found from 27th July to 10th September were all of 
small size, 7 mm. by 4 mm. to 15 mm. by 10 mm., and their spawn-spirals of 
proportionate size, 4 mm. by 24 mm. to 6 mm. by 60 mm. On 11th October 
large individuals were abundant as well, but none of them showed any signs 
of breeding. On this occasion LZ. bilamellata showed a much wider distribu- 
tion than heretofore, being plentiful from the upper Fucus zone to the 
ordinary spring-tide low-water line, whereas its previous range was from the 
latter to the upper Laminarian zone only. 
A, tuberculata showed a corresponding difference in size: the winter 
individuals were large and laid large spawn-spirals, whilst the summer and 
autumn forms were small, and the one spawn-spiral found during October was 
of a proportionate size. 
The very great difference in size between the larger winter-spring and- 
- the smaller summer—autumn forms points to the latter being the offspring of 
the former, and as the latter were breeding there seems no doubt that during 
this year, at any rate, two generations of LZ. bilamellata and of A. tuberculata 
have been produced. 
If these phenomena are of normal occurrence, it would appear that 
bilamellata breeds twice during the first year of its existence but only once a 
year aiterwards. 
The summer-autumn material of twberculata is insufficient to allow of any 
definite inferences being drawn, but what there is points to the same state of 
affairs as has been inferred for bolamellata. 
Alder and Hancock remark that there is great disparity in size in 
bilamellata, but they give no indications as to whether the smaller and larger 
forms were found simultaneously or at different times of the year, though they 
do hint at a double-breeding period. They also mention the occurrence of 
forms of intermediate size, thus giving the hint that the larger is merely an 
older stage of the smaller form, though they do not bring out this point. 
Note on the Nudibranchiate referred to above as Lamellidoris bilamellata 
(Jinn.).—The forms referred to above as Lamellidoris bilamellata (Linn.) seem 
to be intermediate between the two forms described by Alder and Hancock 
as Doris bilamellata, Linn., and Doris pilosa, Miill. 
In habitat and size these two species closely resemble each other, the 
former being found “on and under stones between tide marks,” the latter 
“in shallow water and between tide marks”; whilst the size of the 
former is from } in. to 1} in. by half as broad, of the latter } in. to nearly 
1; in. All the Bute specimens were found between ordinary tide marks 
