472 REPORT OF COMMISSIONER OF FISH AND FISHERIES. [18] 



large and few in number. What is meant here by tlie term yelk spheres 

 must also be explained. We denominate as yelk splieres those large, 

 finely granular masses of protoplasm which are involved in a delicate 

 matrix of germinal protoplasm. The ultimate grannies or splierules 

 which compose these spheres or yelk masses are altogether different, 

 vastly more minute, and are the same as what we have called yelk 

 spherules and granules. The large yelk masses are very clearly seen 

 in the shad's egg, that of the herring, and in El acute, but not so clearly 

 in any other forms known to me. In many types the yelk is almost 

 homogeneous under a low power. In Oyprinoids it is finely granular, 

 and again wholly different from what is seen in the eggs of Clupeoids 

 and Gadoids. These distinctions are important, and not less so is the 

 distinction drawn between the mode of formation of the germinal disk 

 of the Gadoids and Clupeoids. The germ disk of Gadus is wholly devel- 

 oped from the external germinal layer of the vitellus, that of the Clu- 

 peoids is ai)parently not entirely so formed, but derives part of its sub- 

 stance from the protoplasmic matrix involving the large yelk spheres 

 or masses below it. 



The germinal pellicle, cortical layer, has certain common characters in 

 all the forms, however ; these are its superficial position and the vesic- 

 ular or refriugent bodies it incloses prior to the developuient of the disk. 

 In the eggs of the shad and of the herring the cortical or germinal layer 

 contains large refriugent bodies, different from the vesicles which occur 

 in the same layer in the ova of Oadus, I'ylosurus, and Cybium, in the last 

 of which I have watched their slow disappearance and apparent absorp- 

 tion into the surrounding germinal plasma. In this i)rocess they become 

 gradually smaller and finally disappear under the influence of impreg- 

 nation. It would seem as if these refriugent structures were somewhat 

 similar to those seen in the germ of Aeipensemttliemm, and described as 

 islands by Salensky. In Clupea and Alosa, as the peri])heral germinal 

 matter is gradually gathered into a depressed, somewhat conical germi- 

 nal disk, the refriugent globules or spherules which were originally dis- 

 tributed over the whole vitellus become less numerous sind mostly dis- 

 api)ear, except over a portion of the vitelline surface and in si)ots usually 

 near the margin of the disk. After the disk has segmented into a large 

 number of cells and advanced somewhat beyond the morula stage, these 

 relringent spherules have disappeared entirely. The space figured un- 

 derneath the germinal disk in the yelk of the egg of Clupea harengus by 

 Kupft'er is probably a product of the hardening reagents used, and is not 

 to be regarded as a latehra in the sense of the structure of that name 

 found in the ovum of birds. Actual sections of several species of fishes of 

 very early stages of development have served to convince me of the cor- 

 rectness of this interpretation. Germinal matter which does not take 

 ])art in segmentation lies below the disk, as shown by Q^Uacher, and ex- 

 tends over the vitellus as an almost structureless membrane, Dotterhaut 

 of (Ellacher. It is this membrane which protects the vitellus and forms 



