355 



sperm of any of the starfish. However, by changing the constitution of the sea 

 water he succeeded in getting impregnations (in some cases 50 per cent.) 

 between S. ;ji07J(/rfff».s- 2 and Asterms ochracea. Segmentation was normal; 

 the h\rv8e developed into blastulse and gastrulte, some showing the differ- 

 entiation of the intestine. Many other experiments in hybridizing fishes 

 have been recorded. These, however, were all between nearly related 

 species, mostly among the domesticated salmonidge and cyprinidse. It would 

 not be to the point to pass these in review here. For a good summary of 

 these the reader is referred to Ackermann ('98). 



METHODS. 



The method of effecting the crosses and the precautions taken to pre- 

 vent contamination with other sperms, were in all cases essentially the 

 same. The sexes of the same species were kept in separate aquaria. The 

 eggs were expressed into well sterilized watch glasses after which the milt 

 was added. Before adding the milt a sufficient number of eggs were taken 

 from the lot and placed in a fingerbowl of water, as a control. The 

 fertilized lot was also placed in a fingerbowl and allowed to develop there. 

 After the per cent, and character of impregnation was determined and the 

 development well along in segmentation, changes of water sufficiently 

 frequent to insure normal conditions for development were made.^ All 

 dishes, pipettes, etc.. were thoroughly sterilized, first with hot water and 

 then with 95 per cent, alcohol. Notwithstanding the fact that it was 

 found that little danger of contamination existed, the precautions were 

 strictly observed. In not a single instance was there any suspicion that 

 the eggs were not fertilized by the desired sperm. 



1 I wish to call attention to one defect in the methods of rearing the hybrid 

 eggs. It may be objected that while the reaiing of the eggs in the fingerbowl may 

 be satisfactory for Fundulus and some other species it is not normal for a hybrid 

 egg having a sperm from a species that has, for instance, pelagic mode of life during 

 its developmental stages. This unnatural condition may, therefore, in part at 

 least, be responsible for the failures in the development, or even the particular 

 stages at which development ceases. This objection, so far as we know, may or may 

 not be of value. I see no way to avoid this experimental error, since it is not prac- 

 ticable to cater to the demands of one of the parent species without, theoretically 

 at least, infringing on the other. It may bo said, however, that many of the species, 

 especially those on which most stress has been laid, have been successfully reared 

 by this method, e. x., all the species of Fundulus, the two species of Sticklebacks, 

 and the I wo species of Menidia. It is the belief of the writer that this objection 

 may be disregarded. 



