80 ILLINOIS STATE ACADEMY OF SCIENCE 



that are radially arranged around the lumen of the eso- 

 phagus. These chambers seem to end blindly at their 

 posterior ends, which are in somite 14, or at the anterior 

 margin of 15. In most species commonly studied in the 

 laboratories, the esophageal wall in somite 10 is evagin- 

 ated into two lateral pouches, one on each side, often 

 called esophageal pouches, which retain the communica- 

 tion between their cavities and the lumen of the eso- 

 phagus. The longitudinal chambers with, their separat- 

 ing lamellae extend into these pouches between the 

 muscle and epithelial layers for a distance which varies 

 in the different species. Ultimately the cavities of the 

 chambers open into the pouch cavities and a definite com- 

 munication is established. In one species, and in only one 

 of those commonly studied, Lumbrlcus terrestrls, in each 

 of the two somites next posterior to the pouches there 

 are paired lateral swellings of the chambered wall which 

 superficially resemble the pouches in somite 10 in size 

 and form. This results in the presence of three pairs of 

 lateral expansions of the esophageal tube which super- 

 ficially resemble each other somewhat, and have led to 

 the very common statements concerning three pairs of 

 glands. 



These paired inflations of the esophagus are in somites 

 10, 11, and 12. They are not separate glands, but are 

 simply parts of one glandular structure, developed in 

 the wall of the esophagus in somites 10 to 14. They cer- 

 tainly are not three pairs of pouches or diverticula open- 

 ing into the esophagus as often stated. Marshall and 

 Hurst's Zoology and a few other text-books that have 

 adopted the statements contained in it are most nearly 

 correct in their statements concerning the gland or 

 glands, but make no mention of the continuation of the 

 gland development in somites posterior to the 12th 

 somite. 



We will now consider some of the more common errors 

 found in the text-book statements concerning this part 

 of the worm. A new text-book which appeared in 1923 

 states that the esophagus begins in the "6th segment and 

 continues posteriorly as a thin-walled, undifferentiated 

 tube to the 14th segment where it connects with the crop 



