162 PROCEEDINGS OF UNITED STATES NATIONAL MUSEUM. [188^. 



circulation of salmon embryos. — A dis(5ussion of some of the pathological 

 pheuomena observed while salmou embryos are uuder the care of the 

 fish-culturist seem to me to be in place here. 



Shortly after hatching many of the young fish in the hatching troughs 

 sometimes show whitish spots on the yelk-sac. If examined under 

 the microscope it is plain that these spots consist of coagulated or dead 

 yelk material. Very often the capillaries in the vicinity of these spots 

 are found to be occluded and filled with clots of blood, as if the vessels 

 had been bruised. In other cases it is found that the capillaries of the 

 liver are occluded so that that organ, which is visible on the left si le of 

 the embryo through the integument, assumes a whitish, abnormal color. 

 Closer examination reveals the fact that the blood no longer circulates 

 through the liver, and that the tissues of the organ are practically dead, 

 as indicated by the white color which they assume. These conditions lead 

 to the death of the affected embryos in great numbers. The causes which 

 seem productive of such abnormalities have not been determined with 

 certainty, but it would seem probable that blows or knocks received by 

 the sac from careless handling or the violent and too rapid flow of 

 "water over the young fish, so as to carry them violently against fixed 

 objects in the trough, are probably very hurtful and productive of the 

 changes noted. 



Still other abnormal changes in the yelk-sac may be noticed here. 

 The most serious is that characterized by the distension of the epiblastic 

 covering of the sac with fluid so that it is lifted up from contact with 

 the yelk more or less extensively. Usually, this distension only affects 

 the ])osterior extremity of the sac, but occasionally specimens are ob- 

 served in which there is a space all round the yelk between the latter 

 and the epiblastic sac. Sometimes free-blood corpuscles which have 

 escaped from ruptured vessels are found floating about in the fluid con- 

 tained in the cavity described. At other times, an extension of the back 

 part of the 3 elk proper may be prolonged backward into the outer sac, 

 which may become constricted so as to embrace part of the yelk. As 

 the anterior part of the yelk is then absorbed, the ijosterior constricted 

 part is finally left hanging to the abdomen by a sort of j)edicle formed 

 by the outer sack. This finally drops off and the young fish survives. 

 The spot where the stalk breaks off" on the under side of the embryo 

 heals up and the young fish seems none the worse for having lost i)art 

 of its yelk, except that it has probably not grown quite so large or so 

 rapidly as its more fortunate fellows. 



The plate illustrating the foregoing article is number XII of the pres- 

 ent volume. 



