834 STRUCTURE AND DEVELOPMENT OF LEPIDOSTEUS. 



We have first noticed the pyloric caeca arising as outgrowths 

 of the duodenum in larvae of about three weeks old, and they 

 become rapidly longer and more prominent (Plate 40, fig. 62, .). 



The portion of the intestine behind the vitelline duct is, as in 

 all the Vertebrata, at first straight. In Elasmobranchs the lumen 

 of the part of the intestine in which a spiral valve is present in 

 the adult, very early acquires a more or less semilunar form by 

 the appearance of a fold which winds in a long spiral. In Lepi- 

 dosteus there is a fold similar in every respect (Plate 38, fig. 53, 

 sp.v.\ forming an open spiral round the intestine. This fold is 

 the first indication of the spiral valve, but it is relatively very 

 much later in its appearance than in Elasmobranchs, not being 

 formed till about three weeks after hatching. It is, moreover, in 

 correlation with the small extent of the spiral valve of the adult, 

 confined to a much smaller portion of the intestine than in 

 Elasmobranchii, although owing to the relative straightness of 

 the anterior part of the intestine it is proportionately longer in 

 the embryo than in the adult. 



The similarity of the embryonic spiral valve of Lepidosteus to 

 that of Elasmobranchii shews that Stannius' hesitation in accept- 

 ing Miiller's discovery of the spiral valve in Lepidosteus is not 

 justified. 



J. Mliller (Ban u. Entwick. d. Myxinoideii) holds that the so- 

 called bursa entiana of Elasmobranchii (i.e., the chamber placed 

 between the part of the intestine with the spiral valve and the 

 end of the pylorus) is the homologue of the more elongated 

 portion of the small intestine which occupies a similar position 

 in the Sturgeon. This portion of the small intestine is no doubt 

 homologous with the still more elongated and coiled portion of 

 the small intestine in Lepidosteus placed between the chamber 

 into which the pyloric caeca, &c., .open and the region of the 

 spiral valve. The fact that the vitelline duct in the embryo 

 Lepidosteus is placed close to the pyloric end of the stomach, and 

 that the greater portion of the small intestine is derived from 

 part of the alimentary canal behind this, shews that Miiller is 

 mistaken in attempting to homologise the bursa entiana of 

 Elasmobranchii, which is placed in front of the vitelline duct, 

 with the coiled part of the small intestine of the above forms. 

 The latter is either derived from an elongation of the very short 



