294 
SUMMARY OF CURRENT RESEARCHES RELATING TO 
cortex or pallium is accompanied by a richer and more abundant com- 
missural system. This growing commissural system from the dorsal 
part of the enormous pallium not only finds in the £ commissura dorsalis ’ 
a shorter path, but a clearer scope for longitudinal extension than the 
ventral commissure provides ; and thus we have pallial fibres invading 
and subsequently superseding the dorsal limb of what was previously 
the hippocampal commissure. 
“ Pallial commissural fibres probably first make their appearance in 
Beptiles, and form a very insignificant constituent of the ventral com- 
missure. In Monotremes and Marsupials these fibres become extremely 
abundant, and swell the proportions of the ventral commissure enor- 
mously. But in Eutheria a rapidly increasing proportion of these fibres 
forsake the commissura ventralis, and form the new £ dorsal commissure 
of the pallium ’ — the corpus callosum — which throws the £ parent ’ com- 
missure into insignificance. The remnant of the commissura ventralis 
is known in man by the somewhat misleading name £ anterior com- 
missure.’ ” 
INVERTEBRATA. 
Sources of Error in Plankton Method.'" — Prof. C. A. Kofoid dis- 
cusses the Hensen method, which consists essentially in drawing a silk 
net vertically through the water. Its accuracy depends upon the 
efficiency of the silk in really catching the organisms. Experiments at 
the Illinois Biological Station show, however, that the leakage is great. 
The method is satisfactory only for the larger forms, such as the Entc- 
mostraca and the larger Botifera and Protozoa. For the smaller and 
often very abundant “ planktonts,” such as Melosira, Peridmiim, Dino- 
bryon, Pajoliidium , Scenedesmus, Euglena , TracTielomonas, and Chlamydo- 
monus , the Hensen method is wholly inadequate. From water in which 
these smaller forms were not extremely abundant the silk retained 
218,200 organisms per cubic metre, while the catch of the Berkefeld filter 
indicated 767,556,000 planktonts in the same amount. “The plankton 
lost by leakage is of prime importance, for it is composed very largely 
of minute Algae, which constitute a fundamental link in the cycle of 
aquatic life. Any attempt to unravel the complex interrelation of the 
constituents of the plankton, or to correlate its ever-progressing changes 
with the factors of its environment, must be based upon reliable data. 
Biological theory and aquiculture alike demand improvement in the 
plankton method.” 
Heleoplankton.f — Dr. O. Zacharias uses this term for the plankton 
of ponds and pools, which is in some ways different from that of lakes. 
It is, so far as is known, richer in species. There are fewer Diatoms, 
but a larger number of Desmids and Protccoccacese ; and there is a 
much more abundant occurrence of Botifers and CeriodaphniaB. Detailed 
lists are given. 
Freshwater Fauna of Canary Islands.;— M. Jules Bichard gives a 
list of the Phyllopoda, Cladocera, Copepoda, Ostracoda, Polyzoa, and 
Botifera which he observed in the freshwater pools of the Canaries. 
* Science, vi. (1897) pp. 829-32. f Zool. Anzeig., xxi. (1898) pp. 24-32. 
t Comptes Rendus, exxvi. (189S) pp. 4S9-41. 
