514 
SUMMARY OF CURRENT RESEARCHES RELATING TO 
us that to find the common ancestor of similar closely allied species of 
Echinoids, we have to go a very long way back, but in the case of the 
cyclostomatous Bryozoa, great structural differences may be produced 
in only a few, or even perhaps within a single generation. 
The author gives examples which show that variations in this group 
are of very different value from those on which genera are based in some 
other groups of Invertebrates. 
The study of the species with which Dr. Gregory has to do leads 
him to doubt the correctness of Mr. Bateson’s views as to discon- 
tinuous variation. He finds that, if we compare the forms of Bryozoa 
that lived in one particular zone, the species are discontinuous ; but if 
we compare the forms that lived in successive zones, the species are 
continuous. Variation in this case is therefore continuous in time, and 
discontinuous in space. The general evidence of the fossil specimens, 
and the great difference of opinion as to the range of specific variation 
tend to show that most of the forms of Cyclostoma have arisen by slow, 
imperceptible, continuous variation. 
The classification of the Cyclostoma is next discussed, and an 
arrangement is adopted which may perhaps be only temporary. The 
greater part of the catalogue is taken up with the systematic account of 
the species. The British Museum contains fine species of Jurassic 
Bryozoa, both English and foreign. 
Arthropoda, 
a. Insecta. 
Development of Wing-Scales and their Pigment in Butterflies 
and Moths.* — Mr. A. G. Mayer treats of his subject in the following 
order : — (1) The general development of the wings and scales ; (2) the 
development of the pigment within the scales; and (3) the probable 
physical and chemical nature of the pigments. In addition to the known 
facts regarding the order of development of the colours, the author has 
shown that the transparent condition of the wings corresponds to the 
period before the scales are formed, and to the time when they are still 
completely full of protoplasm. The white condition is caused by the 
withdrawal of the protoplasm from the scales. After the protoplasm 
has completely withdrawn, the so-called blood of the pupa enters them, 
and soon after this the wing becomes of a uniform dull yellow or light 
drab colour. The mature colours are due to chemical changes in the 
fluid itself. Proof, which must be taken to be satisfactory, is presented 
to show that the scales are formed from modified hypodermis cells, and 
are therefore truly homologous with the hairs of Arthropods. The 
membrane of the pupal wings exhibits two sets of foldings — one parallel 
to the trend of the nervures, and the other at right angles to it. In 
either cross or longitudinal sections these foldings appear as a regular 
series of ridges, and a single scale arises from the crest of each ridge. 
Evidence is adduced tending to prove that the pigments of the scales 
are actually derived by chemical processes from the blood, or hremolymph, 
of the pupa. The reasons for this belief are that, during the period of 
the formation of pigment, nothing but hsemolympli is found within the 
scales ; in all butterflies and moths the first colour to appear is a dull 
* Bull. Mus. Comp. Zool., xxix. (1896) pp. 209-36 (7 pis.). 
