170 GARRISON. 



12.8 fx. The cirrus is found retracted in most segments, but in a few it is 

 extruded beyond the margin of the segment to a distance of about 25 /*, the 

 extruded portion being about 8 /u broad at its base and tapering. 



The vagina opens immediately posterior to the male orifice, into the common 

 genital cloaca, which is rather shallow and projects at the most but a few (15 

 to 20) IX beyond the lateral line of the' segment. Close to its outer extremity 

 the vagina presents a well-marked dilatation, the receptaculum seminis, which 

 measures 60 /j, long, and 28 fi broad, being only about one-half the length of the 

 cirrus pouch and reaching not one-half the distance from the lateral border to 

 the ventral excretory canal, whereas, in Krabbe's specimen, according to both 

 Leuckart's description and Holzberg's drawing, the receptaculum seminis extended 

 nearly the entire length of the vagina, reaching nearly or quite to the median 

 line of the segment. 



From the dilated portion, the vagina pursues a course inward and slightly 

 caudad to the median line, where it turns sharply caudad to join with the oviduct, 

 the conjoined tube becoming surrounded by the shell gland, and receiving the 

 duet from the yolk gland to form the ootype. The uterus, so far as its structure 

 can be made out in the sexually active segments, appears to consist of a median 

 cavity composed of a number of pouches. The exact arrangement of these pouches 

 and the manner of their gradual extension throughout the segment could not 

 be determined clearly in the sections made, but it seems that the primitive uterine 

 structure gradually extends outward through the parenchymatous tissue of the 

 segment, dividing and subdividing as it progresses, and that small portions, 

 containing one, two, or three eggs each, then become constricted off and lie encased 

 in the parenchyma. The egg-balls form around these pinched-off portions, and 

 their inner, granular zone immediately surrounding the eggs would seem to 

 represent the original uterine structure. 



The following description of the eggs and egg-lialls is based upon a study of 

 material digested in a solution of hydrochloric acid and pepsin. Both the egg- 

 balls and the eggs themselves presented a very different and undoubtedly a much 

 more natural appearance when so treated than when dehydrated, stained, cleared, 

 and mounted. In the segments mounted in balsam, either in toto or in sections, 

 the balls themselves are shrunken, the outer, lighter zone blends with the sur- 

 rounding tissue and is not clearly distinguished, the outer shell is marked only 

 by the light area immediately surrounding the embryo and the inner shell is 

 shrunken close around the onchosphere. 



In the digested segments the egg-halls become separated at what appear to be 

 natural lines of demarcation between their own structure and that of the sur- 

 rounding parenchyma. The individual egg-balls thus set free are round to ovoid 

 and vary considerably in size, measuring from 200 to nearly 400 fi in diameter. 

 They present a clear, comparatively structureless outer zone and an inner, denser 

 and more darkly staining . area, the latter containing the eggs, which may be 

 one, two, or three in number, most often two. Numerous small (8 /i) calcareous 

 corpuscles appear within the inner and outer zones. 



If digestion is allowed to proceed further, the egg-balls themselves are broken 

 up and the individual eggs are set free. The six-hooked onchosphere is inclosed 

 within two envelopes. The outer envelope is extremely thin and delicate and is 

 easily broken up by slight pressure on the cover glass or removed by a little 

 longer digestion. It tapers to a rather sharp extremity at each end and measures 

 about 120 /i in length by about 48 yu in breadth. The inner shell is rather tliin 

 and easily distorted and broken, but is considerably thicker and stouter than 

 the outer shell. It is nearly colorless, but has a light yellomsh-brown tint. 



