NOTES ON SOME EMBRYOS OF CHLAMYDOSELACHUS ANGUINEUS OARM. -97 



and the "anterior end " of Rück ERT. On the surface of the blastoderm the 

 cells are arranged epithelially. Most cells of the blastoderm are rich in yolk 



granules, but at the bottom of the blastoderm they 

 have only a coarsely granular cytoplasm. The 

 blastodermic cells are added from the periphery 

 by the merocytes with fine yolk granules, as may 

 be seen from cut 1, which has been composed from 

 two consecutive sections. I have also found a cell 

 simply resting on the floor of the segmentation 

 cavity ; but I cannot say for certain whether it ori- 

 ginated from the periblast or from the blastoderm. 

 Besides the stages mentioned above I have also 

 obtained a gastrula, which was oval in form and 3 

 mm. in length. I have nothing special to add^about it, as it was like the gas- 

 trula of any other shark. 



The youngest batch of embryos was obtained from a specimen 170 cm. long, 

 which was brought to the University on the 26th of May (1896). There were 

 six embryos 32, 35, 43, 48, 50, and 60 mm. long respectively. Each embryo 

 was attached to its large yolk-sac by means of an umbilical cord, which allowed 

 considerable movement to the embryo. The circulation in the yolk-sac could be 

 clearly traced and is reproduced in figs. 1 and 2. On leaving the umbilical cord 

 the artery and the vein run in opposite directions. The former receives on its 

 course a number of smaller veins from the two poles of the yolk-sac, and divides 

 finally into three main branches. The artery runs for some distance without 

 giving off any branch, and then divides into two main vessels, which after run- 

 ning for a short distance parallel to each other, forms at last, on the opposite 

 side of the yolk-sac, an elongated, irregularly shaped arterial ring, from which 

 numerous small vessels radiate towards the periphery. The arterial ring just 

 mentioned is still wide apart in the embryo of 32 mm., but in one of 43 mm. its 

 two halves almost touch each other ; but in other respects there is no change 

 in the circulation. The embryos themselves are transparent, and the large 

 liver-lobes with their blood vessels, the cardinal veins, and the trunk vessels can 

 be seen from outside. 



The embryo of 32 mm., the smallest one I have got thus far, may be com- 

 pared with Balfour's stage M. The umbilical cord is 7 mm. long and 2.5 mm. 



Cut 1. Zeiss 4 DD. 



