76 ILLINOIS BIOLOGICAL MONOGRAPHS [270 



cuts off only a flat segment, and the margin thus left seems drawn in, partially 

 rounding and obhterating the opening to the intestine. The mouth is small, 

 appearing as a hole in the ventral wall. 



The most striking detail of the whole body structure is, perhaps, the com- 

 plex reproductive system and viviparous habit. The yolk glands lie next to 

 the intestine and are opaque to such an extent as to be easily distinguishable 

 from the other organs. The ovaries and testes are inconspicuous except during 

 a short period of especial activity. A number of specimens each bearing 

 several developing worms, were examined. In one of these, twelve embryos 

 could be seen, seven in the right and five in the left uterus. They were closely 

 packed and most were somewhat curled up, the anterior end sharply bent on 

 the posterior. The movement was mainly a constant stirring, the several 

 worms gliding over each other more or less, and to some extent changing their 

 position in the body. The mother was finally killed, cocaine being used to 

 produce anesthesia. By this method, the regions of greatest contraction were 

 made out. The head and the region posterior to the pharynx are drawn toward 

 the anterior middle part which very greatly increased in diameter, making a 

 heavy knob-like portion. These contractions drove all the embryos to this 

 region where they were tightly massed. Another specimen showed seventeen 

 embroyos on the right side and twelve on the left. These were large, one- 

 fifth the total length of the body of the parent, but were not so confined as the 

 younger specimens. The wall of the uterus is heavy and not elastic, but so 

 enlarged as to give ample space within. All the young worms were active and 

 incessantly hurrying from one end to the other, crawling over each other in 

 the most promiscuous way. This enlargement of the uterus pushed toward the 

 center both the intestine and what little remained of the yolk glands. The 

 testes had almost completely disappeared so that the main portion of the body 

 on each side was occupied by the large transparent uteri. These, however, were 

 extended only as far forward as the head region. The extra space needed was 

 gained by a dorsal swelhng, the central upper surface being extraordinarly 

 extended, making the shape of the animal most grotesque. The two uteri 

 connected with each other across the middle fine by uterine ducts but there 

 never seemed to be any intermingling of the individuals from the two sides. 

 This was evidently due to the fact that the duct was too small to admit of the 

 passage of large worms. By the time the embryos are ready for birth the 

 duct is stretched but even then the tendency is to pass to the exterior rather 

 than across the body, since in the outward direction the resistance is less. The 

 young worms in this specimen and in the one mentioned above showed clearly 

 two of the later stages of growth. In the first, the embryos were not long in 

 proportion to width, the head was not at all marked off from the body regions, 

 and the intestine was nearly clear. In the second example, the embryos were 

 much more elongate, the head tapered off shghtly and the intestinal wall was 

 visible as a hght gray with many very regular globular cells. The eyes in both 

 were prominent. In the older worms the pharynx was also fully developed and 



