ON THE PAIRED NEPHRIDIA OF PROSOBRANCHS. 623 
Fie. 22.—Puncturella spec.? viewed from the left side after removal 
of the shell. 14. 
1 
Fic. 23.—Transverse section through the pericardium and both kidneys of 
Fissurella greca. 2. 
Fic. 24.—Horizontal section through the pericardium and both kidneys of 
Tectura spec.? 32, 
Fic. 25¢.—Transverse section through the pericardium and both kidneys of 
Patella coer, 2. 
Fic. 25 4.—Transverse section through the pericardium and the left kidney 
of Patella coer. +99. 
Fic. 26.—Transverse section through the right kidney of Fissurella 
nubecula, showing the genital duct opening into the right kidney, which 
also contains eggs. 
Fie. 27.—Transverse section through the pericardium and both kidneys of 
Emarginula Huzardi. #2. 
Lenses and eye-pieces used with Abbé’s camera lucida.—Zeiss, oc. 1 
(achr.), obj. a3 (achr.) = 22. Zeiss, oc. 1 (achr.), obj. 16 mm. focal dis- 
tance (apochrom.) = 22. Zeiss, 2 (apochrom.), obj. 16 mm. focal distance 
(apochrom.) = +92, 
The above-mentioned eye-pieces and lenses were used for the drawing of 
the figures of microscopic sections; the whole series of the apochromatic 
objectives, 8 mm., 4 mm., and 2 mm. immersion, were used during the course 
of this investigation, with apochr. eye-pieces 6 and 8. The drawings of dis- 
sected specimens were done with Nachet’s dissecting stand and a camera 
lucida. 
