4()() J. DUESBEllG 



oratory of ^^'oocls Hole, Massachusetts and I am ti;lad 1 have this 

 opportunity of expressing to Professor F. R. Lilhe my gratitude 

 for his kind hospitaUty. The results obtained were practically 

 the same for all species; unless otherwise stated, my description 

 will refer to Fundulus. My material consisted of embryos of 

 this fish of various stages from that of nine hours after dry 

 fertilization up to the ninth day. To Professor Stockard I am 

 indebted for a demonstration of this procedure of fertilization. 

 Specimens of all stages, up to hatchmg, of both kinds of the 

 perch and of the trout were also procured. My series are un- 

 fortunately incomplete, for I experienced at first many difficul- 

 ties in obtaining good preparations; these troubles were over- 

 come only when most of the material was used up. 



The fixatives employed were first, the mixture of formol- 

 bichromate after Regaud, secondly, Benda's fluid and several 

 modifications of it. 



After treatment with Regaud 's fluid, a good number of the 

 embryos of all species mentioned showed excellent preservation 

 of the chondriosomes, but even then, they could hardly be used 

 for an embryological study. This difficulty is proportionally 

 greater in the younger embryos. The outlines of the different 

 organs are usually poorly defined. Some tubular organs (the 

 intestine or the Wolffian ducts, for example) shrink considerably 

 in many specimens. The limits of the cells cannot, for the 

 most part, be distinguished at all, even in those cases in which, 

 after fixation with Benda's fluid, they appear as plainly as they 

 do between the epidermic cells, as represented in figure 2a. 

 The yolk has a great tendency to swell and consequently to 

 dislocate the cell-structure, — a phenomenon which I had al- 

 ready experienced (cf. Duesberg, '15) and which I observed again 

 this summer, in dealing with ascidian-embryos. In these, the 

 swelling of the yolk is especially noticeable in certain stages and 

 in certain cells. 



The technical results obtained on these fish-embryos seem to 

 be, within certain limits, independent of the respective duration 

 of action of the formol-bichromate mixture and of the bichromate 

 solution subsequently used, provided the total duration of ac- 



