190 EMBRYOLOGY OF THE LOWER VERTEBRATES oh. 



In Teleosts the early development agrees closely with that of the 

 ganoids, only a doubt exists whether the definitive pancreatic duct 

 (Duct of Wirsung) may not be formed by a fusion of the two ventral 

 ducts rather than by the persistent right duct alone. During later 

 stages great differences arise between different members of the group. 

 In some (Silurus, Esox) the complex forms a single compact gland, 

 in others (Scomber, Gyprinus) it becomes divided into a number of 

 independent lobes, in others, including the majority of the more 

 familiar Teleosts, it becomes greatly branched and is diffused in the 

 substance of the dorsal mesentery while in still others (Labridae, 

 Syngnathus) the condition resembles that of the ganoids a large part 

 of the organ being intrahepatic (Laguesse, 1894). 



Fig. 109. — Dorsal view showing tudimeuts of dorsal pancreas and lung in larvae 

 of Protopterus (stages 32 and 34). 



I, lung ; op, operculum ; pa.d, dorsal pancreas ; p.b, postbranchial body ; p.f, pectoral limb ; 

 v.c, visceral cleft rudiment. 



In Lung-fishes the three typical rudiments make their appearance. 

 In Protopterus the dorsal rudiment (see Fig. 109, A, pa.d) is a solid 

 outgrowth (hollow in Lepidosireri) from the gut- wall, usually rounded 

 in form but occasionally elongated in an antero-posterior direction 

 as in the specimen figured (Fig. 109, A). The attachment to the 

 gut becomes rapidly constricted to a narrow stalk and a cavity 

 develops in the interior of the rudiment. The ventral rudiments 

 appear a little later, as solid projections one on each side of the 

 attachment of the bile-duct to the gut. The two ventral rudiments, 

 as they increase in size, meet and fuse dorsal to the bile-duct, and 

 later on the dorsal surface of the right ventral rudiment comes in 

 contact and fuses with the ventral surface of the dorsal rudiment. 

 The stalks of the three rudiments remain as three ducts, the two 

 ventral opening just posterior (original right rudiment) and anterior 



