No. I.] EMBRYOLOGY OF THE I SO TOD CRUSTACEA. 65 



the identification of the Porcellio and Armadillidiiini studied, 

 I can only say that they are the common forms of these genera 

 occurring in New England, and lacking the literature necessary 

 for a definite identification, I cannot state positively that they 

 are the species named above. 



The methods employed were comparatively simple. After 

 experimenting with a number of fixing reagents, such as corro- 

 sive sublimate, hot water, picro-sulphuric acid, and others, I 

 finally adopted an alcoholic picro-sulphuric acid, which gave ad- 

 mirable results, producing no distortion of the ova, and pre- 

 serving the cells in an almost perfect manner. Picric acid is 

 dissolved in 70% alcohol until saturation, and two volumes of 

 sulphuric acid are added to every hundred volumes of this solu- 

 tion. The reagent is, indeed, simply Kleinenberg's strong 

 solution made with 70% alcohol instead of with water. For 

 staining the early stages I employed Kleinenberg's haematoxy- 

 lin, generally deeply overstaining, and then carefully washing 

 out in 70% alcohol, acidulated with hydrochloric acid. The 

 stain is washed out more rapidly from the yolk than from the 

 protoplasm and nucleus, which thus became very distinct. In 

 the early stages the eggs thus treated could be cleared in oil of 

 cloves and thus studied, but I found that in later stages, after 

 the cells had reached the surface of the yolk, it was preferable 

 to study them as opaque objects, using direct illumination. 

 When the blastoderm was well formed it was possible, in the 

 larger ova, such as those of Poirellio, Armadilliduun, Ligia, 

 and CymotJioa, to remove it from the yolk and study it as a 

 transparent object after clearing, but in the minute eggs of 

 Jaera, and to a certain extent in Asellus, this method of pro- 

 cedure was not feasible. For sectioning the ova of Jaera, and 

 the later stages of the other forms, the usual paraffin method 

 was employed. In the early stages, before the formation of 

 the blastoderm, the brittleness which the yolk assumed under 

 this method prevented its application to the larger eggs, and 

 for these, after the removal of the egg-membranes, the celloidin 

 method was employed. 



