368 ANDREWS. [VoL. XII. 
The observations at Wood’s Holl were made with a Beck 
jz immersion, which had been carefully chosen from a number 
for its flatness of field, definition, and lack of color, — with apo- 
chromatic eyepieces. 
At the Zodlogical Laboratory of the Sorbonne, Roscoff, Brit- 
tany, where I was enabled by courtesy of M. Lacaze Duthiers 
to make a series of similar observations, the instruments used 
were all of Zeiss, — largest size stand, with Abbé condenser and 
iris diaphragm ; 4.0 mm., and 2.0 mm. immersion, lenses ; with 
4-12 apochromatic oculars. 
While there proved to be nothing to correct in the first 
observations, they were much extended and amplified by the 
second series whose range of magnification brought to sight a 
greater length of filament, also secondary spinnings, or ramifica- 
tions of these, and still other primary filaments far beyond the 
reach of the powers before used. 
The sea-urchin eggs were from two genera ; those obtained 
at Wood’s Holl, from Arbacia ; those used at Roscoff, from the 
common, large, and finely colored species of Echinus found 
along that coast. 
The Arbacia eggs were perfectly normal in their initial 
conditions, and in large proportion developed to a late larval 
stage; they, as well as the sperm, were obtained artificially 
from the animals. The Echinus eggs and sperm were also 
obtained artificially, but, being more hardy, gave, it was 
thought, for that reason more reliable data than Arbacia even, 
although the results in the one case but confirmed those in the 
other. 
The starfish eggs used in both series of observations were of 
the same genus, but of different species. In all the test cases 
the eggs were laid and fertilized naturally in a tank shortly 
after capture. Those collected at Roscoff were sometimes 
from two or more females and two or more males depositing at 
one time. The eggs were, however, protected from too great 
admixture with sperm by instant separation, and afterwards 
carefully washed and then kept in small quantities in 
separate, large dishes in which the water was frequently 
changed. 

