14 
POPULAR SCIENCE REVIEW. 
whole of the posterior two -thirds of the body is filled with 
sperm sacs.* 
With regard to the 64 Sargasso Sea,” the masses of 44 Crulf ” • 
weed which float here are not matted together, but consist of a 
single layer of the feathery branches of Sargassum bacc forum, 
the vesicles of which plant are encrusted with a beautifully 
netted white polyzoon. The patches of weed, varying in shade 
Fig. 2. 
from an olive to 44 a golden tint of olive,” form a lovely con- 
trast with the 44 intense indigo ” of the sea between. One of 
the most perfect examples of protective resemblance is shown 
by the fauna of the 44 G-ulf ” weed, which imitate both in form 
and colour their habitat, so as effectually to deceive both birds 
and fishes who might otherwise prey upon them. A little fish 
— the Antennarius — makes nests in the weed, and a small crab 
which swarms upon the 44 sargasso ” corresponds in degree of 
colour with whatever part it may chance to inhabit. 
* Apropos of this discovery, Mr. Charles Darwin makes, in a long and 
interesting letter in “ Nature,’’ Sept. 25, 1873, some remarks on the males 
and complemental males of certain cirripedes. 
