6 G. O. Sars. 



and Hoyle 1 ), though without any more detailed descriptions 

 or figures. 



The development described in the present paper would 

 seem chiefly to refer to two forms, viz., Nyctiphanes norvégiens 

 and Boreopliausia JRaschü, which both, at times, occur rather 

 abundantly in the Christiania Fjord; but I have also studied 

 all phases of the larval development of a third form, probably 

 Thysanoe'ssa neglecta, the larvæ of which, especially in the 

 more advanced stages, are easily distinguished from those 

 of Nyctiphanes and Boreophausia by their much more 

 slender form. 



As to the method of examination employed, I have 

 always in the first instance examined fresh and still living 

 specimens. It is, indeed, in my opinion, very desirable that 

 such a preliminary examination should, if possible, be in- 

 stituted in all kinds of zoological investigations, whether 

 histological, anatomical or embryological, as many essential 

 features admit of being much better examined in this way 

 than is the case with a preserved material. Only in studying 

 more closely the several phases of cleavage of the ovum and 

 the formation of the embryonic layers, can a suitable prepara- 

 tion of preserved material give a clearer idea than an 

 examination of only fresh material. I have tried several 

 methods of preparation, but that which has given the best 

 results is the following: The ova are to be separated from 

 the material, in which they are contained, and put into 

 pure water, from this into a strong solution of DelafiekPs 

 Hæmatoxylin, in which they may remain for one 

 or two hours. The ova are then taken up and cleaned in 

 weak alcohol, whereupon they are transferred to a solution 



] ) Proceedings of Eoyal Society of Edinburgh, 1888. 



