GANOIDEI. 91 



The i>eculiar flattening out of the embryo over the yolk {vide pp. 8G 

 and 87) is no doubt connected with the mode in which the yolk becomes 

 enveloped by the hypoblast. 



As the posterior part of the trunk, containing the intestine, becomes 

 formed, the yolk is gradually confined to the anterior part of the alimentary 

 tract, which, as before stated, becomes the stomach. The epithelial cells 

 of the stomach, as well as those of the intestine, ai'e enormously dilated 

 with food yolk (fig. 57, st). Behind the stomach is formed the liver. 

 The subintestinal vein bringing back the blood to the liver appears to 

 have the same course as in Teleostei, in that the blood, after passing 

 through the liver, is distributed to the walls of the stomach and is again 

 collected into a venous trunk which falls into the sinus venosus. As the 

 yolk becomes absorbed, the liver grows forwards underneath the stomach 

 till it comes in close contact with the heart. The relative position of 

 the parts at this stage is shewn diagrammatically in fig. 56. At the com->' 

 mencement of the intestine there arises in the larva of about 14 mm. a 

 great number of diverticula, which are destined to form the compact,] 

 glandular organ, which opens at this spot in the adult. At this stage'/ 

 there is also a fairly well developed pancreas opening into the duodenum 

 at the same level as the liver. 



No trace of the air-bladder was present at the stage in question. 



The spiral valve is formed, as in Elasmobranchii, as a simple fold in the 

 wall of the intestine. 



There is a well-developed subnotochordal rod (fig. 57), which, according!) 

 to Salensky, becomes the subvertebral ligament of the adult; a statement n 

 which confirms an earlier suggestion of Bridge. The pronephros (head- \\ 

 kidney) resembles in the main that of Teleostei (fig. 57) ; while the front 

 end of the mesonephros, which is developed considerably later than the 

 pronephros, is placed some way behind it. In my oldest larva (14 mm.) 

 the mesonephros did not extend backwards into the posterior part of the 

 abdominal cavity. 



Bibliography. 



(88) Knock. "Die Beschr. d. Eeise z. Wolga Behufs d. Sterlettbefruchtnng. " 

 Bull. Soc. Nat. Moscow, 1871. 



(89) A. Kowalevsky, Ph. Owsjannikoff, and N. Wagner. "DieEntwick. d. 

 Store." Vorlauf. Mittheilung. Melanges Biologiques tires du Bulletin d. I'Acad. Zotjj. 

 St Petersbourg, Vol. vii. 1870. 



(90) W. Salensky. "Development of the Sterlet (Acipenser ruthenus)." 2 Parts. 

 Proceedings of the Society of Naturalists in the imperial Vniversiiy of Kasan. 1878 and 9 

 (Russian). Part I., abstracted in Hoffmann and Schwalbe's Juhresbcricht for 1878. 



(91) W. Salensky. "Zur Embryologie d. Ganoiden (Acipenser)." Zoologischer 

 Anzeiger, Vol. i., Nos. 11, 12, 13. 



LefidosteusV 

 The ova of Lepidosteus are spherical bodies of about 3 mm. in 



1 Alexander Agassiz was fortunate enough to succeed in procuring and rearing 

 a batch of eggs of this interesting form. He has given an adequate account of the 

 external characters of the post-embryonic stages, and very liberally placed his preserved 

 material of the stages both before and after hatching at Prof. W. K. Parker's and my 

 disposal. The account of the stages prior to hatching is the result of investigations 

 carried on by Professor Parker's son, Mr W. N. Parker, and myself on the material 

 supplied to us by Agassiz. This material was not very satisfactorily preserved, but I 

 trust that our results are not without some interest. 



