214 /\. Oguiiia: 



1. Stomodaeiim (Fore-intestiiiei 



-• Buccal intestiiie. 

 ) Oesophagus. 

 I Crop. 



Proventriciiclus. 



2. Mesenteroii (Mid-intestinei — Stomach or Ventriculiis. 



i Small intestinc or Ileum. 



3. Proctodaeiun (Hind-intestine) » Rectum. 



' Anal piece. 

 The rectum is converted into so-callcd rectal tracheal gills in 

 almost its whole length, except the anal piece, tlie bind most short portion, 

 just before the anus, and swells throughout the canal to the stoutest 

 appearance. There is on the dorsal surface of the stomach a pair of 

 trachii of remarkable size, called dorsal trunks; their peripheral cell 

 contain rieh pigment granules of brownish color. The diameter of each 

 trunk varies according to portion : at the anterior half of the rectum it 

 attains the largest size and therefrom gives off, in both sides, niany parallel 

 branchlets to the rectum. They enter into the rectal papillae or evaginations 

 of rectall wall and form the rectal gills. The hinder part of this trunk 

 again becomes slender, and its extremity extends into the last abdominal 

 blind spiracle on eighth segment. Besides these dorsal trunks another 

 pair of finer trunks, containing no pigments in the wall, is found along 

 the sides of the stomach, in very close contact with it and gives off 

 minute branches to the stomach, while the posterior ends are splited into 

 tufts which also enter the rectum from its ventral side. This second pair 

 of trachii are called visceral trunks; at the anterior part of the stomach 

 they bend upwards, and after crossing each other like the letter x over 

 the stomach, each of them connects with the dorsal trunk on the opposite side. 



Structure of the Rectal Gills. 



The rectum, swelling enormously, is more or less hexagonal in outline 

 on a cross section. On the inner surface the rectum has six double 

 rows of triangulär lamellae or gills which run parallel to the long axis 

 of it, and the hexagonal outline is merely due to this arrangement 

 of gill rows. In a double row of gills every Single gill Stands at an 

 angle less than the right angle against the median line of the row. 

 Therefore, on a cross section through the rectum one finds that either 

 half of a double row is composed of several cut pieces of gills which 

 have been bisected in various positions (fig. 2). A Single gill, or lamella 

 is merely a strong evagination or folding of the rectuiu wall, in which 

 larger and finer tracheal branches of considerable number are imbedded. 

 One may distinguish near the median line of the double row the basal 

 whitish part from the other larger part which is thinner and highly 

 pigmented. They are called respectively the basal cushion and gill 

 lamella (figs. 3 und 4). In addition to Sadones' detailed investigation 



