BAKNACLES ; THEIR FACTS AND THEIR FICTIONS. 395 
any Decapod Crustaceans — for instance, a spider-crab (dfam). 
Cirripedes — though this was once doubted — have eyes in their 
adult stage provided with special optic nerves, but the func- 
tion of this organ is probably limited to the cognizance of 
shadows intervening between them and a source of light. 
Saccular organs, opening externally by orifices, supposed to 
be olfactory and acoustic in function, have been found 
at the bases of the outer maxillse and first pair of cirri respec- 
tively. 
A brief outline of the earlier phases of the life of a Cirripede 
must suffice. In the yelk of its ovum segmentation is com- 
plete, but there is no primitive band — a point in which it 
differs from that of a crab or lobster, which are accordingly 
placed in a separate sub-class by Fritz Muller. The larva 
{Nawplius\ on emergence from the egg, passes through three 
stages, each of which is further modified by a series of moults 
before that it arrives at the adult condition and has “ settled 
down” permanently. This Naujplius form — ‘Hhe extreme 
outpost of the class,” as Fritz Muller terms it — varies so little 
in all the divisions of the Crustacea, be their representatives 
ever so unlike when adult, that in the six orders selected and 
figured for comparison by Haeckel, “ no greater difference ” — 
as he well observes — “ can be detected than in six different 
‘ good species ’ of a genus.” I have figured in the plate two 
instances (figs. 7, 8) of this “common family form of all 
Crustaceans” (gemeinschaftliche Stammform aller Krebse), and 
of their far more differing forms (figs. 6, 9) when adult. 
The organs which undergo the most curious transformations 
while the Naujplius is passing through its three stages are its 
eyes. In the first stage there is only a single simple eye, 
possibly formed by the confluence of two, in the normal position 
in the front of the head ; but in the succeeding stage the 
organ is doubled, but the two eyes, as yet simple, have shifted 
their position backwards. In the third, or pupal stage, the 
eyes remain in the same place, but have now become large 
and compound ; while in the last, or mature stage, they have 
not only moved some way posteriorly again, but have actually 
become again simple and minute, being either confluent, as 
in Lepas, or fairly far apart, as in B alarms. The larva in its 
last or pupal stage (see fig. 6) bears a great resemblance to 
the mature form, except in the size of its eyes and in the 
presence of a pair of antennse in front of them, by which, 
through the medium of a large sucker in their middle joints, 
it is enabled to anchor itself to some object. Though this is a 
voluntary act, the animal cannot for long change its mind 
and “slip moorings,” but eventually remains fixed, “willy- 
