ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 
29 
because of its ready acclimatisation and its comparatively great power 
of resistance to the effects even of severe operations, M. Boutan “ tre- 
panned ” the shells, and introduced minute beads of mother-of-pearl 
through the openings, which he afterwards closed with cement. The 
beads were so placed as to lie between the mantle and the shell, and in 
all cases mother-of-pearl was secreted over their surface. From many 
of the shells really fine pearls were procured. These, though the same 
in chemical composition as natural pearls, of course, have the desired 
orientation in circular layers only on the periphery, since they enclose a 
fairly large nucleus of foreign matter. But M. Boutan maintains that 
his pearls cannot on this account be called false, because even pearls 
which are naturally produced contain a nucleus of undetermined size. 
Cephalic Eyes in Lamellibranchs.* — Dr. Paul Pelsener has found 
that a pair of distinct and well-developed cephalic eyes may occur in 
adult Mytilidae. They are formed by little pits with pigmented walls 
and containing a cuticular lens, thus exhibiting a structure intermediate 
between the eyes cf Trochus and those of Patella. They appear to be 
peculiar to the majority of the genera of the Mytilidae [Mytilus, Litho- 
clomus, Modiolaria), and to the allied genus Avicula properly so-called, 
that is, excluding Meleagrina . They occur in both larva and adult, but 
appear in the larva ( Mytilus ) only after the development of the first 
branchial filament. They are situated at the base and on the axial sur- 
face of the first filament of the internal branchial lamella, and are 
innervated from the cerebral centre. In the larva they lie outside of 
the posterior margin of the velum, and are therefore homologous with 
the larval eyes of Chitons, but not with the cephalic eyes of Gastropods, 
which arise within the velar area. 
Arthropoda. 
a. Insecta. 
Colour-Evolution in the Pieridse.f — Herr M. C. Piepers publishes 
an elaborate paper on this subject. He believes that the most primitive 
colour in the wing-scales of the Pieridae is red, and that colour changes 
take place along a definite liue, influenced, but not determined, by 
external conditions. The course of evolution is such that the primitive 
red tends to fade to orange, yellow, and ultimately white, while simulta- 
neously there is a development of brown or black colour, tho amount of 
black varying inversely with the amount of red. During these stages 
the females may lead the way in colour change (female preponderance) ; 
but as a further stage the black may disappear, and the white greatly 
increase in amount, and in this direction it is always the males which 
lead (male preponderance). Ultimately the white pigment may disap- 
pear, a process which is followed by the loss of the scales themselves. 
While these changes are occurring, there is a simultaneous develojnnent 
of structural colour, which is apparently the last stage in colour-evolu- 
tion. The author seems disposed to regard these statements as true not 
only of the Pieridae, but also of other butterflies, notably the Papilionidae. 
* Comptes Rendus, cxxvii. (1398) pp. 735-6. 
f Tijdschr. Nederland. Dierkund. Ver., v. (1898) pp. 70-289. 
