494 Mr. E. E. Prince on the Nest and 



area. The eyes, in which the lenses are now fully formed, 

 are faintly pigmented with black. Nuclei still persist over 

 the blastoderm, probably periblastic, but they are much 

 reduced in number. Before the close of the seventeenth day 

 the heart pulsates, though slowly and irregularly j more 

 rapidly, however, on the eighteenth, though no hsemal fluid is 

 as yet visible. 



On the nineteenth day a distinct circulation is active. The 

 formation of circulatory channels on the yelk-surface is very 

 readily seen, and coincides with Ryder's description of the 

 embryo of Apeltes *. The venous end of the heart, as in all 

 Teleosteans, is applied to the yelk-surface, and by an exca- 

 vation in the latter a capacious sinus is formed, in which 

 corpuscles are seen vibrating to and fro, with the cardiac pulsa- 

 tions, before a circulation has commenced. Whether these 

 primitive corpuscles originate in the periblast was not deter- 

 mined ; but it certainly is the case that periblast-cells are 

 detached and pass with the hsemal fluid into the heart when 

 the circulation is established. This accords with Ryder's 

 contention (in common with Hoffman, C. Vogt, and others) 

 that the blood is a derivative from the periblast. 



The vascular trunks, ramifying over the vitellus, appear to 

 be simple lacunse hollowed out of the yelk-cortex. In addi- 

 tion to the circulation of the embryonic trunk proper, the 

 subnotochordal, arterial, and the cardinal (venous) trunks 

 (which extend no further than the root of the tail at this stage), 

 there are a subintestinal vein, breaking up apparently in the 

 liver, and two large vitelline vessels. Of the last-named, 

 one emerges behind the heart and the other in the region of 

 the hind gut, the alimentary canal as yet ending blindly. 

 These two capacious vitelline trunks unite in the distal por- 

 tion of the yelk and return by a common large vein, which is 

 joined by numerous lesser trunks, until it reaches the pectoral 

 region, where it pours its volume into the sinus communicating 

 with the heart. 



A complex network of blood-vessels, or, rather, of sinuous 

 lacunse, covers the deutoplasmic globe, and the early approach 

 of the hatching stage is indicated. On the nineteenth day, 

 indeed, the embryo is very restless, the tail being spasmodi- 

 cally flexed and straightened, and vigorous side-to-side move- 

 ments are executed. The pigment of the eyes is more dense, 

 though the trunk is comparatively free from pigment, a few 

 non-stellate black spots merely occurring on the dorsum. The 

 development of the liver and alimentary canal agrees with 



* U.S. Fisli Comm. Report, 1882, p. 643. 



