586 
SUMMARY OF CURRENT RESEARCHES RELATING TO 
Fauna of the Swedish West Coast.* — Mr. C. W. S. Aurivillius has 
made a series of observations on the period of development of the 
invertebrates of the Skager Rack, and the periodicity in the appearance 
of larval forms in that region. His paper is illustrated by elaborate 
tables showing the date of appearance of larval and adult forms in 
the Skager Rack throughout the years 1893-8. The tables show not 
only the day of the month when the forms first appeared, but the depth 
at which they occurred, the temperature and salinity of the water, the 
condition of the tide, and the relative abundance of each form. The 
tables thus not only show the relation of the fauna to the physical con- 
ditions at the time, but also yield data from which may be calculated 
the period of sexual maturity for the different forms, and the rate of 
development. The general results of this elaborate piece of work are 
stated as follows. The fauna of the Skager Rack may be divided into 
two sets : — first, the animals which constitute the genuinely native forms 
(endogenetic animals), and second, those which invade the area from 
elsewhere, or at most are naturalised in it (allogenetic animals). The 
period of sexual maturity is in intimate connection with this division, 
that is, it depends upon the geographical nature of the forms. For the 
purely endogenetic forms the reproductive periods are chiefly influenced 
by the hydrographical conditions of the surface layers of water, and 
this whether the forms be bottom or plankton forms. Of the hydro- 
graphical conditions the temperature is the most important. As to the 
allogenetic forms, whether bottom or plankton forms, their increase 
depends upon the course of the currents which sweep the larvae into 
the Skager Rack. Thus, for example, the northerly current which bears 
the waters of the Gulf Stream and flows from November to March, 
bears with it the characteristic Gulf Stream forms. Thus the periodi- 
city in the appearance of larval forms in the Skager Rack depends upon 
similar causes both in endogenetic and allogenetic forms. In the first 
case it depends upon the fixed times for the appearance of sexual 
maturity;’, in the second upon the periodicity of the ocean currents 
which sweep in organisms from other parts of the ocean. 
Plankton of the Oder.f — Herr C. Zimmer distinguishes (1) eupo- 
tamic plankton, consisting of organisms which flourish in flowing and 
still water, e. g. Rotifers; (2) tychopotamic plankton, consisting of 
organisms from pools and overflow basins, e.g. Entomostraca ; and (3) 
autopotamic plankton, consisting (as far as known) only of Algae. He 
discusses the differences in the fauna which are associated with differ- 
ences in rate of flow, temperature, &c.. of the river. 
Tunicata. 
Coloration of Tunicates J — M. Antoine Pizon finds that most of 
the coloured spots and lines which occur on many Tunicates are due 
to pigment-granules, generally of very minute size (about 1 p in cir- 
cumference), and that these granules in the living animal show very 
rapid movements within the vesicles which enclose them. In Botryllus 
smaragdus, for instance, there are three kinds of coloured elements or 
* Bihang t. Ivongl. Svenska Vetens. Akad., xxiv. (1899) pp. 45-91. v 
‘ [t Preisschrift Philos. Facult'at Tniv. Breslau, Breslau, 8vo, 14 pp. See Zool. 
Centralbl., vi. (1899) p. 739. + Comptes Rendus, cxxix. (1899) pp. 395-8. 
