INTRODUCTION. 5 



Crustacea, and insects, have been brought under control, and made to 

 yield most instructive results, thanks to the skill and perseverance of such 

 observers as Wiismann, Ischikawa, Blochmann, and Platner. The facts 

 wrested from such difficult objects of study may be won only at an 

 enormous expense of time, but that we cannot afford to neglect them 

 on that account has been abundantly shown by the recent papers of 

 Wcismann and Platner. 



The study of these phenomena must be as broad as the range of facts 

 and the nature of the material will permit. The panoramic display to 

 be witnessed in small transparent eggs, like those of the starfish and sea- 

 urchin, reveals the order and relations of consecutive scenes, and thus 

 supplies the needed vantage-ground for comparative study. But each 

 scene is in itself a picture, to be studied not only in relation to what 

 precedes and follows, but also in comparison with corresponding pictures 

 in other eggs. Every variety of form and finish, every contrast or resem- 

 blance, has something to contribute to the general fund of information, and 

 is therefore worthy of the most searching scrutiny. Difficulties of ma- 

 nipulation are seldom insurmountable, and the eggs of Ascaris and many 

 arthropods have shown us how the most forbidding material may be 

 converted into inexhaustible mines of discovery. 



In such considerations we find a sufficient protest against the shiftless 

 tendency to neglect the less inviting sorts of material, and at the same 

 time a reason — not an apology — for the considerable space devoted to 

 the early history of the egg in the present paper. 



The usual prelude of historical summaries has been omitted, but not 

 from any lack of proper regard for previous contributions in the same 

 line of inquiry. This side of the subject has already been liberally dealt 

 with by recent writers. Besides, we are now laboring under a plethora 

 of " literature," which makes it desirable to deal less prodigally in his- 

 torical compilations. This is a deliberate protest, not against the intro- 

 duction of such abstracts and comments as are required in order to place 

 the matter in hand in a clear and impartial light, but against the ex- 

 travagant amount of space often given to the history of the subject, as 

 compared with that devoted to original observation. 



The observations here presented were begun in the summer of 1883, at 

 the Newport Marine Laboratory, and completed in the winter of 1885-86. 

 It was hoped that these studies on " The Development of Osseous Fishes " 



