208 



Mr. F. S. Conant on the Chcetognc 



II. The Diverticula of the Intestine. 



In two of the European species, Sagitta minima and Spa- 

 della cephaloptera, a pair of diverticula are described as 

 occurring at the anterior part of the intestine. In the 

 American forms this structure is more common, being found 

 in three of the nine species about to be enumerated. In 

 S. hispida they appear from the surface as outlined in fig. 4. 

 A cross section through the animal in this region would show 

 the digestive tract composed of three tubes lying side by side, 

 as figured by Grassi for Spadella cephahptera (Taf. vi. 

 fig. 11), of which the middle one is in reality only the 

 oesophagus, as it enters the stomach intestine. The epithelium 

 of the diverticula is the same as that of the intestine, and 

 they seem to be in fact only the prolongations of the intestine 

 anteriorly beyond the point where the laterally compressed 

 oesophagus makes connexions with it. In a variety of 

 S. hispida from the Bahamas the diverticula are reduced to a 

 very small size, and cannot have much function. In the 

 Beaufort hispida and in 8. elegans they may vary according 

 to the individual — in some large, in some small. 



Diagrammatic optical section of the head and neck of S. elegans fi-om 

 above. ilfO, mouth; Oii^, oesophagus ; Z>, diverticula ; 7, intestine. 



An interesting modification of apparently the same structure 

 occurs in S. elegans. In many of the specimens from Woods 

 Holl diverticula are found extending within the digestive 

 tract. Fig. 5 gives a diagrammatic representation of these 



