Physiology of Sagitta bipunctata. 303 
as seen with a lens. The other figures are drawn from the organs seen under 
the microscope, and the determination of the magnifying power was made 
from the calculation of a vision of 74 inches. 
Fig. 1, The Sagitéa, a little larger than its natural size, —a view of its dorsal 
surface: a, the head; 8, first pair of lateral fins ; c, second pair of 
lateral fins ; d, caudal fin ; e, openings of the excretory duct of the 
ovaries ; f, prominence of the seminal cavities. 
Fig. 2. The same animal—view of its ventral surface: g, ventral ganglion 
of the nervous system, seen by transmitted light; , anterior 
branches of nerves, or pharyngeal commissures ; /, posterior 
branches of nerves ; /, the ovaries seen by transmitted light (they 
are here little developed) ; m, the anus. 
Fig. 3. A view of the under-side of the head, with the hood in a state of 
complete expansion: a, the hood; 4, inferior surface of the head ; 
c, prominences furnished with bristles; d, the mouth; e, the hooks 
seen through the lateral parts of the hood: they are closed together ; 
Jf, commencement of the trunk, 
Fig. 4. Profile view of the head in a young specimen ; the hood expanded : 
a, prominence on the upper surface of the head, beneath which is 
situated the right eye ; 6, the hooks of the right side in their state 
of repose ; c, the trunk. 
Fig. 5. Upper view of the head. The hood is retracted, and the hooks are 
in their state of erection : aa, superior and lateral points of inser- 
tion of the retracted hood; 6, the free margin of the hood ; c, the 
superior and lateral parts of the head and the hooks exposed; 
d, transparent view of the cephalic ganglion; e, the anterior ce- 
phalic nerves; /, the nervous loop formed by the posterior cephalic 
nerve ; g, the eyes. 
fig. 6. Under view of the head, with the hood retracted and the hooks erect : 
aa, portion of the hood; 8, the prominences furnished with bristles ; 
c, the margin furnished with bristles ; d, the mouth; e, the muscles 
of the hooks, forming a hemispherical projection. 
Fig. 7. A ventral view of the posterior parts of the body, magnified five to 
six times, and turned so as to exhibit a larger portion of the left 
lateral surface: a, pair of posterior fins; 6, caudal fin; ¢, anus ; 
d, ovary seen by transmitted light, exhibiting the curve which it 
describes above; e, prominences of the seminal cells. 
Fig. 8. Excretory apparatus of the seminal fluid; it is seen on two sides, 
magnified from ten to twelve diameters, and exposed as has been 
said in the text: a, the superior muscular band seen withinside ; 
b, the two canals with their rounded apertures opening into the 
seminal cells; c, the cavities, the prominences of which are hol- 
lowed: at their bottom is seen the opening by which they commu- 
nicate outwardly, in the form of a fissure. : : 
Fig. 9. Excretory apparatus of the seminal fluid of the left side, more power- 
fully magnified: a, the canal; 4, its opening, conducting into the 
seminal cells; c, cavity of the prominence; 4, external opening 
visible on the sides of this cavity. 
Fig. 10. An aggregation of cells (seminal globule), which is subsequently 
changed into spermatozoa (magnified more than seventy dia- 
meters). 
Fig. 11. Indication of avery common state of development of the spermatozoa, 
and more advanced than the preceding; it is not mentioned in the 
text. In the centre are seen the cells of the primitive seminal 
globule diminished in volume (magnified ninety-five diameters). 
Fig. 12. Mature spermatozoa, magnified 420 diameters. 
