DAVAINEA MADAGASCARIENSIS. 169 



meters. The youngest segments are only aboiit 50 /i long, there being' about 20 

 in 'the first millimeter after their appearance. Gradually increasing in length 

 and breadth the segments attain a maximum breadth of 1.5 millimeters about 

 15 centimeters from the tip of the head and at this place the length of the 

 segments lias increased to something less than 1 millimeter, i centimeter of 

 the length of the strobila containing from twelve to fifteen segments. Thereafter, 

 the segments increase in length,' remaining about the same in breadth, for a 

 distance of from 10 to 12 centimeters, when they are about square. The lengthen- 

 ing then 'Continued, "while the breadth shows a tendency to decrease, the segments 

 at the same time beginning to take on the "barrel" shape which becomes more 

 pronounced as we approach the posterior extremity. The terminal gravid seg- 

 ments, which comprise some 10 to 12 centimeters of the length of tlie strobila, 

 measure about 2 to 2.5 millimeters long by 1 to 1.5 millimeters bi'oad. ' 



' The total number of segments in specimen 305 A is 'about 600. 

 The younger segments tend to a trapezoidal form, the posterior border being 

 somewhat broader than the anterior and overlapping thd anterior extremity of 

 the succeeding segment. 



-The genital fores are not prominent and in the yoimger segments are situated 

 near the cephalic extremity of the lateral border, later holding a: more posterior 

 position, but always well forward of the mid-plane of the segments. Tliey are 

 unilateral with occasional transpositions. Usually the pore will be found on 

 the opposite side in only a single segment, occasionally in two or three, and in 

 one case (specimen '305 D) the pore was found transposed in about 70 consecutive 

 segments. 



INTERNAL ANATOMY. 



Excretory canals. — The ventral excretory canals can be followed throughout 

 the length of the strobila, connected at the posterior border of each segment by 

 a transverse canal and attaining maximum diameters of 40 by 20 ix. The dorsal 

 canal is about half the size of the ventral and can be followed in sections almost 

 throughout the strobila. It is placed in a plane considerably mediad to that of 

 the ventral canal, and both canals are situated a considerable distance to the 

 median side of the lateral nerve. The vagina and vas deferens pass between 

 the two canals and behind the lateral nerve in all the segments in which the 

 relative position could be determined. 



Genital organs. — As indicated above, the segments develop sexually very early 

 in the strobila, the primordia of the genitalia appearing as a dark line in the 

 median field almost with the first appearance of segmentation and while the 

 segments are still only about 160 by 50 fi and about 2.5 millimeters from the tip 

 of the head. 



The testicles appear early, when the segment is scarcely 500 /z broad and 200 /j, 

 long, and before the female genital glands have been clearly difi'erentiated. They 

 are about 50 in number, scattered through the parenchymatous tissue, internal 

 to the excretory canals, and are roughly divided into a dorsal and a ventral 

 layer. The vas deferens is extremely long and coiled, extending from the cirrus 

 pouch to about the median line, the coils filling an area from 60 to 120 /i broad. 

 The cirrus pouch is distinctly bottle- or gourd-shaped, situated in the antero- 

 lateral corner of the segment, with its long diameter (neck) directed outward 

 and backward. It measures from 120 to 160 /x in length by 64 to 100 /x in 

 breadth. The narrowed neck of the pouch may be nearly straight but more 

 frequently is curved like the neck of a gourd, its concavity being posterior. 



After entering the pouch the vas deferens makes two or three irregular coils 

 and enters the cirrus, which is about 80 fj. long with a maximum breadth of 



