26 BULLETIN OF THE UNITED STATES FISH COMMISSION. 



by means of which it ai^pears that this sinus is pushed out more to the 

 right and subdivided into minor channels, the corpuscular contents of 

 which flow towards the heart, pouring their contents into i' s venous 

 end. At 'lirst ic can scarcely be said that there is a circulation ; the cor- 

 puscles appear and the pulsation or pumping action of the heart causes 

 an oscillation or swaying back and forth of these corpuscles. As soon 

 as the aortic channel underneath the chorda dorsalis is broken through 

 the blood commences to j)our through the sinus from the tail end head- 

 wards, as the cycle is now complete. The cardinal vein is formed about 

 the same time. From it the feeders of the sinus, now the vitelline ves- 

 sels, are soon developed and they now spread out over the yelk as nar- 

 row channels, becoming more and more numerous. They at first spread 

 out over the aboral pole of the yelk, and a great common venous chan- 

 nel begins on the left side of the embryo and goes round to the right 

 side over the yelk like a girdle, to feed the heart. Into this equatorial 

 vascular girdle the blood pours from the hemi-meridioual, aboral chan- 

 nels. This asymmetrical or right-hand side channel is gradually pushed 

 forward until it encircles the head below and in^frout of the point where 

 the mouth will ajjpear. The yelk is now becoming less in bulk, and 

 finally the vessels arrange themselves so that the main venous channel 

 lies in the middle line, while the feeders which get their supply from 

 under the body of the embryo trend outwards and somewhat back- 

 wards, but as they turn to traverse the lower face of the yelk they one 

 and all trend forward to converge and join the great venous channel. 



The above arrangement may be described as a difluse omphalomeseraic 

 system, and differs from that of Zoarces described by Eathke, in being 

 asymmetrical, and from that of the pike as described by Truman, in the 

 disposition of the vessels, their more meridional course, and in their 

 being fed from the under side of the body in a diffuse manner. It 

 differs widely from that of birds and reptiles and sharks in there not 

 being any differentiation of venous and arterial trunks over the blasto- 

 derm. Also from the system described by Yogt in Coregonus pakm, in 

 that the latter is comparatively rudimentary, while as compared with 

 the cod, smelt, moon-fish, and Spanish mackerel, there is the broadest 

 and most fundamental difference of all, in that in every one of the latter 

 there is nothing whatever which can be considered as representing an 

 omphalomeseraic or vitelline system of vessels. 



Gensch* has lately studied the development of the blood in Zoarces 

 and Esox by means of sections, and has reached the conclusion that the 

 blood corpuscles in these forms are developed by budding oft' from the 

 hyi^oblast as it has appeared to me in the case of the stickleback. This 

 announcement at first appeared almost incredible to the writer, but upon 

 investigating the form above described it appeared perfectly reasonable, 

 but it must be borne in mind that there are no less than four or five dis- 



*Die Blutbildung auf dem Dottersack bei Knoclienfisclien. Arcli. fiir Mik. Anat., 

 xis, pp. 144-136. 



