470 Illinois State Laboratory of Natural History. 



becomes necessary to correct the statement made in the 

 original description that there is but one sperm-sac (Smith 

 '96, p. 405), for while it is true concerning the specimen of 

 which transverse sections were made and in which the repro- 

 ductive organs were somewhat degenerate, in the other 

 specimen there are two sperm-sacs, one containing the 

 sperm-reservoir and the greater part of the spermiducal 

 apparatus, and the other, a considerably smaller one, belong- 

 ing to the other side of the worm, containing no trace of a 

 sperm-duct. Each of the posterior pair of lateral vessels of 

 X extends backward into the sperm-sac of its own side, 

 forming long loops in its course. In the specimen of which 

 transverse sections were made and in which there is but one 

 sperm-sac the posterior lateral vessel of X which is in the 

 side containing the sperm-sac extends posteriorly into that 

 organ for a distance of several somites, while the correspond- 

 ing vessel of the other side extends posteriorly for a similar 

 distance, and is closely invested by a layer of tissue which 

 doubtless represents a degenerate sperm-sac. 



In the individual most carefully studied somites XI-XVII 

 have no perigastric vessels, but there seem to be two pairs of 

 gastric vessels in each (PL XLL, Fig. 4). There is an ante- 

 rior pair of lateral vessels without cceca in each of somites 

 XVIII-XXIII, which leave the dorsal vessel as perigastric ves- 

 sels but unite with the intestinal plexus instead of the ventral 

 vessel. There is considerable variability in the positions at 

 which these vessels enter the intestinal wall. It may be any- 

 where from the ventral part of the intestine to a position two 

 thirds of the way from the ventral to the dorsal region (Fig. 5). 

 The posterior pair of lateral vessels in each of these somites 

 are gastric vessels. In each somite the ventral vessel is con- 

 nected with the ventral part of the intestinal plexus in the 

 two regions that are most closely related to the two pairs of 

 lateral vessels. A considerable number of somites posterior 

 to XXIII have not been sectioned, but of some of the poste- 

 rior ones sections have been made, the most anterior of which 

 has two pairs of perigastric vessels with ccecal diverticula : 

 an anterior pair, connecting the dorsal vessel with the ventral 



