326 
SUMMARY OF CURRENT RESEARCHES RELATING TO 
y. General. 
Plankton-Studies.* — Prof. E. Haeckel begins bis account of plankton- 
studies with an historical sketch, in which the first date is 1845, when 
Johannes Muller began his memorable “pelagic fishing with a fine net.” 
From him Haeckel and many others received their first impulse. After 
recording the various plankton studies conducted by himself and others, 
Haeckel draws a number of distinctions between Plankton and Benthos, 
Plankton and Nekton, Haliplankton and Limnoplankton, and so on. 
“ Plankton ” was originally defined by Hensen as including those animals 
which drift in the sea. 
The plankton organisms are classified as follows : — 
A. Protophy tes : Chromaceae, Calcocyteae, Murracyteae, Diatomese, 
Xanthelleae, Dictyocheae, Peridineae. 
B. Metaphytes : Halosphaereae, Oscillatoriae, Sargasseae. 
C. Protozoa : Infusoria, Foraminifera, Badiolaria. 
D. Coelenterata : Medusae, Siphonophora, Ctenophora. 
E. Helminths : Chaetognatha. 
F. Mollusca : Pteropoda, Heteropoda, Cephalopoda. 
G. Echinodermata : larvae. 
H. Articulata : Annelids like Tomopteris and Alciope. 
Crustaceans such as Copepods, Ostracods, 
Schizopods. 
Insects, Halobatidae. 
J. Tunicata : Copelata, Lucidiae, Thalidiae. 
K. Yertebrata : e. g. ova and larvae of fishes. 
Haeckel then discusses the sometimes homogeneous, but oftener hetero- 
geneous character of the plankton ; its annual, monthly, daily, and 
hourly variations ; the difference in quality in different climatic zones, 
the influence of currents ; the methods of study. Throughout there is 
vigorous criticism of Hensen’s plankton studies. 
Position of Nerve-Centres.| — M. A. Julien is of opinion that nerve- 
centres may be reduced to three types : the ventral (of Radiates), the 
dorso- ventral (of Annelids and Mollusca), and the dorsal (of Vertebrates). 
He formulates a general biological law in the following terms : — There is 
a constant relation between the position of the principal nerve-centres 
and that of the chief sensory and locomotor organs. Thus, in Asteroids, 
the locomotor system is formed by a circular canal which is placed 
around the mouth, and gives rise to five ventral canals; each of these 
canals carries tactile organs, and is often terminated by a visual organ. 
The circumanal canal is in relation with a nerve-ring, which gives 
rise to five ambulacral trunks. Illustrations are given explaining how 
this law may be applied to the other groups cited ; a physiological 
explanation of the anatomical law is offered, and the corollary 
urged that the Vertebrate is not an Annelid on its back, or vice versa. 
Protoplasm and Life.J — Under this title Mr. C. F. Cox has published 
a critical and historical essay on “ protoplasm and the cell-doctrine,” 
* Jenaische Zeitschr. Naturwiss., xxv. (1890) pp. 232-336. 
t Comptes Rendus, cxii. (1891) pp. 741-3. 
X New York, 1890, sm. 8vo, 67 pp. 
