INVERTEBRATE ZOOLOGY. 79 



grow smaller and less mature, the youngest being at the anterior end where 

 they may be seen dividing off and becoming more distinct. If all the pro- 

 glottids are broken from the scolex in a living tape-worm, the scolex alone re- 

 maining, it will in a few weeks produce a second series of proglottids. 

 On the edge of each proglottid may be seen a slight projection containing 

 a minute oi^ening. This is the genital papilla and is used both for fer- 

 tilization and for the passage of the eggs. The papillae of some tape-worms 

 occur all on one side, but here they generally alternate, those of adjacent 

 •links being on opposite sides. In other species each proglottid is double, hav- 

 ing genital papillae on each edge. 



50. Preparation of a proglottid. Select a mature link and cut it off 

 with scissors, leaving portions of adjacent links attached. Place it between 

 two slides, hold it up to the light and apply gradually increasing pressure 

 with the thumbs and forefingers. Watch this procedure carefully and stop at 

 the first indication of cracking. A well preserved link will usually sustain 

 as much pressure as may be applied by this means. As it becomes gradually 

 more transparent, the different organs will become distinct, the most con- 

 spicuous being the dendritic uterus filled ^\^th eggs. A dark line passing 

 from this out to the genital i)apilla indicates the otu'dttct and the male vas 

 deferens. The staining and mounting should follow the rules given in 42. 



5 I , General anatomij of j)i-()(/l(>ftids. The anatomical relationships of 

 parts are complicated and difficult to follow. In general the organs are simi- 

 lar to those of Trematodes. jiltered in shape to fit the rectangular outline of 

 the links, and the lateral position of the genital opening. The successive 

 links represent different stages of development, and hence in order to fully 

 understand the parts, several preparations should be made and compared. 



(a) An "immature" link. This refers to one taken about in the jniddle of 

 the animal, where the links ai-e generally much broader than long. In such a 

 link the male organs are mature, while all the female organs, ovary, yolk 

 glands, etc., are small but distinct. Notice : testes, many small round masses 

 giving a mottled appearance to the lateral regions of the links ; vas deferens, 

 a slightly wavy tube leading to the genital i«ipilla and ending in a small 

 pouch containing the eirrhus or organ of copulation ; ovary, an oval mass, 

 central in position, but on the posterior margin : from this last an oviduct 

 runs parallel to the vas deferens, and opens at the genital papilla ; yolk glands. 

 lying along the posterior edge of the ovary ; uteivis, a tubular sack extending 

 from the ovarj' through the center in an anterior direction — this may or may 

 not bear small lateral branches : nephridia. a pair of tubes running along the 

 lateral margin and united in each segment by a transverse tube. 



