BULLETIN OF THE UNITED STATES FISH COMMISSION. 27 



tiuct hypotheses as to the origin of the blood in embryos, besides this 

 one, so that the matter cannot be considered as settled. In all cases 

 j where there was no vitelline circnlation I have not been able to arrive. 

 ' at a satisfactory conclusion in regard to the manner in which the matter in 

 the yelk sack was absorbed; whether by transudation, amoeboid migra- 

 tion, or gemmation, and it therefore still remains an unsettled problem. 

 It will not, it appears to me, satisfy the facts in the case, that because 

 the blood originates by gemmation from the hypoblast in those cases 

 where there is a vitelline circulation, it should so originate where such 

 a circulation is absent. The corpuscles of the stickleback are at first 

 irregular and amoeboid in outline, and do not acquire their oval shape 

 for some time, or till about the tenth or twelfth day, when the young fish 

 is ready to leave the egg, which is strong evidence in confirmation of 

 Geusch's view as to the manner of origin of the blood of types with a 

 vitelline or omphalomeseraic circulation. In other forms it has always 

 appeared to me that there was strong ground for believiug that the 

 blood had its origin, in part at least, in the lacunjB which make their ap- 

 pearance in the mesoblast of the body late in embryonic life. 



The heart retains its horizontal position in the stickleback for a longer 

 time than in any other form which I have studied, and is an instance of 

 what Professor Cope would call retardation in the development of a 

 part; indeed, the comparative histories of the several si^ecies investi- 

 gated by the writer afford most beautiful illustrations of both i^rinciples 

 enunciated by the learned biologist just referred to, namely, accelera- 

 tion and retardation of development, both synchronous and heterochro- 

 nous. This long retention of an embryonic character is, however, to be 

 considered as caused to some extent by the development of an omphal- 

 omeseraic system, and as in some degree dependent upon the correlative 

 interdependence of parts serving a common purpose. 



Kupfier's vesicle was found to be present, and at one time I believed 

 that it became the allantoid vesicle, but owing to the opacity of the eggs 

 I failed to trace it satisfactorily to myself. The allantoid, however, occu- 

 pies the usual position, and is large and inclosed by a proper cellular wall. 

 The course of the intestine when the embryo is nearly ready to hatch is 

 marked by a greenish color. The blood very soon becomes reddish in 

 color before the fish leaves the egg, a character which it has in common 

 with no other form studied by me, except perhaps the sculpin. In all 

 other cases investigated by me, the blood is developed after the embryos 

 leave the egg. There is also a well-developed system of vascular loops 

 existing in the natatory folds along the back and belly before the fish 

 is ready to leave the egg, while the branchial vessels, arches, and oper- 

 cula are already in an advanced condition at this period, all of which 

 are accelerated conditions of development as compared with other forms. 



When the embryo leaves the egg there are already lateral sensory 

 organs developed on the skin. If the young fish is allowed to assume 

 its normal position in a cell, and the microscope is applied, looking down 



