Enibryologij of Salpa. By W. K. Brooks. 9 
lateral pencils directing light far beyond the axial one greatly 
enlarge the diameter of the proper light disk, and an excess or 
false aperture is delineated. My present standpoint is, that every 
method, without exception, hitherto employed in measuring angles 
of aperture is exceedingly erroneous. An aperture mapped out on 
a screen shows very instructively the outline of the false aperture 
and the true one, as obtained with the slit. The first is faintly 
portrayed as an outer circle of light while the bright disk given by 
the slit takes an oval form within the other. This is more difficult 
to manage than the slit with the ordinary sector method and lamp, 
by which it is easy to focus and adjust for the thickness of cover. 
I give the result on three object-glasses made nearly twenty 
years ago, viz. a Jth, an -^th, and a whose apertures were 
stated to be 100°, 130°, and 170° ; these measured with the sht 
gave 56°, 92°, and 100°. 
I invite fair discussion on the question ; as one of science, it 
should cause no feeling of the animosity displayed by a few whose 
only motive appears to have been to endeavour to show me in the 
wrong. 
IV. — Embryology of Saljpa. By W. K. Brooks, Ph.D. 
Plate CXLIV. 
Students of the embryology of the various forms of Tunicata are 
so numerous and active at present, that the naturalist who refrains 
from publishing any new facts which he may acquire until the 
figures necessary for their illustration can be prepared, is very apt 
to find that they are no longer new. The following brief abstract 
of the more important points in the history of the development of 
Salpa has therefore been drawn up, as the precursor of a more 
extended description which is now in preparation. 
At the time when the Salpa-chain escapes from the body of the 
solitary form, each individual of the chain contains one ovum, 
which is enclosed within a capsule of epithelial cells, and is sus- 
ended in the sinus system of the "zooid" on the neural side, 
etween the stomach and the atrial orifice, by means of a guber- 
naculum, by which it is attached to the wall of the branchial sac. 
(See Fig. I.) 
The ovum shows no trace of a vitelline membrane ; the yolk is 
composed of transparent protoplasm without granules, and the 
germinal vesicle contains no dot, but seems to be homogeneous. 
Impregnation takes place through the action of tbe spermatic 
filaments which are discharged into the water by the zooids of 
