95 
I beg to tender my sincere thanks to the following gentlemen, 
who have assisted me in identifying the different forms mentioned 
in this paper or by giving me informations of the litterature con- 
cerning the questions treated here, or otherwise: Mag. sc. K. Hen- 
riksen, Professor Ad. S. jensen, Professor W: fohannsern, 
Inspector W. Lundbeck, Mr. H. Lynge, Cand. mag. K. Ste- 
phensen, Dr. C. Wesenberg-Lund, Vice-Inspector H. Winge 
and Mr. Worm-Hansen. A special thank is due to Professor 
E. B. Poulton, Oxford, for the most valuable literary references 
about the double-headed butterflies a. 0., he so kindly has sent 
me. Finally I beg to express my sincere thanks to the Carls- 
berg-Fond for affording me the means for the illustrations of 
this paper. 
Additional Note. A case of protective coloration among Bivalve 
Molluscs ought still to be mentioned, viz. Pteria (Electroma) Zebra 
Reeve. The young specimens of this species are beautifully coloured 
With alternating dark and light stripes. This coloration produces an 
astonishing resemblance to the hydroids to which they are found 
attached. (See H. Lynge. Marine Lamellibranchiata. The Danish 
Expedition to Siam 1899—1900. Mém. Acad. R. d. Sci. de Copen- 
hague. 7. Sér. V. 1909. p. 142. Tab. II. Fig. 16—18. N. Odhner. 
Mollusca. Res. of Dr. Mjoberg's Swedish Sci. Exped. to Australia 
1910—1913. K. Sv. Vetensk. Akad. Handl. Bd. 52. 1917. p. 16. 
PLA. Figs. 6-8). 
Reference should be made to the following papers which I have 
been able to consult only after this paper had been sent to print: 
:J. Crozier. On the Immunity Coloration of some Nudibranchs 
(Proc. Nat. Acad. Sci. Washington. II. 1916. p. 672—5) and W. H. 
Longley: Observations upon Tropical Fishes and Inferences from 
their adaptive Coloration. (Ibidem, p. 733—7), and the same authors 
Paper on: The Significance of the Colors of Tropical Reef Fishes 
(Yearbook of the Carnegie Institution, Washington, No. 15. 1916; 
p. 209—12). Another paper by the same author: The Colors and 
Color Changes of West Indian Reef-fishes (Journ. of Experimental 
Zoology. 1917) I have not seen as yet, likewise a paper by Potts 
