288 W. K. Brooks—Cephalopod Siphon and Arms. 
ready stated, it is only when the zone of maximum force is 
widened, by raising the central magnet, that fig. 7 is stable 
without the repulsion of the electric current. In the new form 
of the experiment, on the other hand, while the force near the 
center of the field increases directly as the distance, towards 
the margin it increases still more rapidly, and in this case 
but one or at most but two of the magnets take their place 
near the center, as we should expect. 
In our ignorance of the es structure of a molecule, 
or the law of the variation of the force that controls the mo 
tions of its several parts, we offer no 5 Spiniba as to which mode 
of experiment (both being confined to plane he yyitien 
the better illustration of the still unknown forms of atom 
and molecular configuration. Equation (2), However is fat 
simpler than equation (1). 
Both modes of experimenting are readily carried out, if the 
cirgnane? A precautions are taken; but the attempt fails when 
are imperfectly magnetized. Our water was drawn 
from service pipes under considerable pressure, and we were 
obliged to renew it every ten or fifteen minutes ; otherwise the 
magnets failed to move freely. Whether this would be the 
case with water freed from an excess of air, we have not de- 
termin n our modification, we used one or two Bunsen 
cells, with five turns of No. 16 ¢ copper wire in a coil of 15 
e.m. diameter. A single one-fluid cell is sufficient. 
The work already accomplished is only qualitative ; but we 
pe ose to continue the investigation (both by experiment and 
y analysis) with regard to the stability of certain figures, un- 
der the various modifications of the experiment. 
Haverford College, Pa., June, 1880. 
Art. XXXI.—WNotes from the Chesapeake Zoological Laboratory 
of the Johns Hopkins University. 
No. L—Thte puua oA, the Acetate Siphon and Arms ; 
WHILE studying the fates of thé squid (oligo Pealit), 
I fortunately procured embryos at stages which fill gaps in the 
account which has been given by Grenacher, and which seem to 
place the homology between the cephalopoda and the ordinary 
mollusca in a very clear light, and eth a diagram of an early 
stage of peoiss's! nara of the squid, and another of a gastero- 
pod, in a corresponding stage. ithout discussing the literature 
of the subject I will pass at once to the description of the 
figures. 
