6 PEOCEEDINGS OF THE NATIONAL MUSEUM. vol.64. 



iiicliiied to regard the strobiles of the first group as older than those 

 of the second group. 



Anatomy of a proglottis. — The genital apertures are irregularly 

 alternate, and situated at about the anterior third of the length; in 

 a segment 3.5 mm. in length the genital pore was 1.2 mm. from the 

 anterior end. The cirrus is long and slender, bulbous at base and 

 spinous. The vas deferns is voluminous, situated antero-medially 

 to the base of the cirrus-pouch in a bend of the vagina. The testes 

 fill the median region of the proglottis from the ovary to the anterior 

 end. The vagina opens at the connnon pore anterior to the cirrus. 

 In some cases it makes a loop-like bend around and in front of the 

 dense mass of coils of the vas deferens, then follows the median line 

 to near the posterior end, where it narrows to a slender sperm duct 

 near the shell gland. The ovary forms two wing-like lobes, sym- 

 metrically placed with reference to the median line at the extreme 

 posterior end of the proglottis. The shell gland is enclosed between 

 the posterior halves of the lobes of the ovary. The vitelline glands 

 are conspicuous, deeply staining bodies, as seen in whole mounts, Ijang 

 along the lateral margins of the proglottis, from the ovaries to the 

 anterior end. Outlines of the uterus are not clearly shown in my 

 preparations; ova in ripe proglottides are distributed throughout 

 the interior in front of the ovary, in some cases most abundant from 

 the middle to the anterior third, where they may appear as a dense 

 mass. The ova spherical, thin shelled, often collapsed in mounted 

 segments, and 0.015 mm. in diameter, more or less. 



Garcharhinus milb erti. 



Collected in three of the years from 1915 to 1922 : On two dates in 

 July, 4 and 13, with many free proglottides, 2 sharks, length 112 

 centimeters; on six dates in August (on one date, few in 1 of 6 

 sharks), 1 to 15, with many free proglottides, in each of 7 sharks, 

 112 to 210 centimeters in length, maximum length of strobile 18 mm. ; 

 on one date in September, 10, length about 20 mm,, the anterior un- 

 segmented portion slender and armed with short, bristly spines. 



(U.S.N.M., Helm. Coll. 7659.) 



0. comniersonii. 



1922, August 7 : 2 from a 112 centimeter shark. 



1923, August 6 : 7, maximum length 60 mm., and a large number 

 of free proglottides, from a 290-centimeter shark. 



August 7 : 19, maximum length 40 mm., from a 321 -centimeter 

 shark. 



August 15 : 115, maximum length 30 mm., from a 153-centimeter 

 shark. One in each of 3 out of 7 sharks examined on three other 

 dates in August. 



