ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 
179 
characteristic of plants as opposed to the more complex pigments of 
animals. Finally, he notices that colouring-matters which belong to 
the right half of the spectrum, or are not primary colours, are charac- 
terised by their chemical complexity, and their association with complex 
tissues in differentiated organisms. They are notably absent from 
simple organisms. 
Function of the Retina.* * * § — Herr C. Hess calls attention to Herr G. 
F. Weinland’s bookf on this subject. Weinland’s view is that the 
visual purple is destroyed by light, and the change induces volume 
changes which express themselves as pressure upon the cones of the 
retina, varying intensities of light giving rise to corresponding varia- 
tions in pressure. The pressure thus produced is conveyed by the 
fibrils of the optic nerve to the brain. Colour blindness depends upon 
a diminution of delicacy of pressure-transmission. All sense-stimuli 
are similarly regarded as leading to differences in pressure which are 
transmitted along the nerves. 
Tunicata. 
Rouble Larva of Diplosoma.t — M. Maurice Caullery discusses the 
morphological interpretation of the double larva in the compound 
Ascidians of the genus Diplosoma. His conclusion is that the larva 
does not correspond to a division of the embryo, but to a combination of 
oozoid and blastozoid. The latter arises on the former by the ordinary 
processes of budding which set in at the end of the embryonic period. 
It is a phenomenon of accelerated development , of heterochronism, which 
results in an exchange of viscera between the two individuals. 
Digestive Gland ill Simple Ascidians.§ — Herr Hans von Winiwarter 
has studied the anatomical relations of the so-called digestive gland in 
Corella par allelo gramma and Phallusia scabra by the method of sections. 
He finds that the gland consists of a network of tubules composed of a 
single layer of cells and a structureless basal membrane. The gland is 
continued into excretory canals of similar structure, which open by 
several (five or six usually in Corella) pores into the mid-region of the 
stomach. 
The Genus Sigillina.|| — M. Maurice Caullery describes the structure 
of Sigillina australis , and discusses the systematic position of the genus. 
It agrees in many respects with Polyclinidae, but the heart is situated 
in the abdomen , on the right side, to the interior of the digestive loop ; 
and the testis consists of eight to twelve ampullae, also to the interior of 
the digestive loop. In these two respects, Sigillina agrees with the 
Distomidae. Caullery proposes to unite Polyclinopsis and Sigillina in a 
special family, Polyclinopsidae, a name already proposed by Gottschaldt, 
and to place the family between Polyclinidae and Distomidae. 
* Biol. Centralbl., xvi. (1896) pp. 175-6. 
t ‘ Neue Untersuchungen fiber die Funktionen der Netzhaut, nebst einem 
Versuche einer Theorie iiber die im Nerven wirkende Kraft im Allgemeinen,’ 
Tubingen (no date) 123 pp. 
X Comptes Rendus, cxxi. (1895) pp. 776-80 (3 figs.). 
§ Arch. Biol., xiv. (1896) pp. 261-73 (1 pi.). 
U Comptes Rendus, cxxi. (1895) pp. 832-4. 
