190 EMBRYOLOGY OF THE LOWER VERTEBRATES CH. 



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 

 at differences arise between different members of the group. 

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

 in others (Scomber, Cyprinus) 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 tiie organ being intrahepatic (Laguesse, 1894). 



B 



Fi<.. 109. Dorsal view showing indiments of dorsal pancreas and lung in larvae 

 of Protopterus (stages 32 and 34). 



/, lung; 



, open-ilium ; ]*i.d, dorsal pancreas ; p.b, postbranchial body; p.f, pectoral limb; 

 ,il deft rudiment. 



I n I. u HIT- fishes the three typical rudiments make their appearance. 

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

 oin growth .'hollow in Lepidosiren) from the gut- wall, usually rounded 



in form but occasionally elongated in an antero-posterior direction 

 the specimen figured ( Kig. 109, A). The attachment to the 

 gut beenmes rapidly constricted to a narrow stalk and a cavity 

 ops in the interim- of the rudiment. The ventral rudiments 

 appear a littl.- later, M .-olid projections one on each side of the 

 aitachment. of the bile-dnel to the ^uf. The two ventral rudiments. 

 ;is th \ UKireBM m si/e, meet and fuse dor.sil to the bile-duet, and 

 later on the dorsal surface of the ri^ht \entral rudiment mines in 

 COBtecl and fuses \\ith the y.-ntra! M:I face of the dorsal rudiment. 

 The stalks of the three rudiments remain as three ducts, the l\\o 

 \ent r, il opemirj JUSI |". -i. -nor (original ri^hl i iidmieiit ) ami antei ior 



