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 1\ inches. 



Fig. I. The Sagitta, a little larger than its natural size, — a view of its dorsal 

 surface : a, the head; b, first pair of lateral fins ; c, second pair of 

 lateral fins ; d, caudal fin ; <?, openings of the excretory duct of the 

 ovaries ; /, prominence of the seminal cavities. 



Fig. 2. The same animal — view of its ventral surface : g, ventral ganglion 

 of the nervous system, seen hy transmitted light ; /i, anterior 

 branches of nerves, or pharyngeal commissures ; /f, 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 ; b, 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 ; 

 /, commencement of the trunk. 



Fig. 4. Profile view of the head in a young specimen ; the hood expanded : 

 o, prominence 07i 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 : a a, superior and lateral points of inser- 

 tion of the retracted hood ; b, 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 : 

 a a, portion of the hood; b, 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 ; b, caudal fin ; c, 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 a})paratus of the seminal fluid of the left side, more power- 

 fully magnified : a, the canal ; b, its opening, conducting into the 

 seminal cells ; c, cavity of the prominence ; d, 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 a very 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 semiiiJil 

 globule diminished in volume (magnified ninety-five diameters). 



Fig. 12. Mature spermatozoa, magnified 420 diameters. 



