418 Dr. H. J. Hansen on the Morphology of the 



with a large number of the animals, as also with the investi- 

 gations and opinions of the anatomists, embryologists, and 

 systematists with reference to the main details of the morpho- 

 logy and classification of the forms with which we are con- 

 cerned. The greater part of these investigations have been 

 carried out with the aid of the dissecting-microscope, often 

 with a magnifying-power of one hundred diameters. My 

 experiments show that it is often possible to study the articu- 

 lation and composition of the mouth-parts much better with 

 this instrument than by means of higher magnification under 

 the compound microscope ; the latter, however, is much more 

 frequently employed. A reagent of which T have very often 

 availed myself is a strong cold solution of caustic potash, in 

 which the preparations are placed until the internal tissue is 

 partially or completely decomposed and can be washed away 

 in glycerine. I have frequently found it very advantageous 

 to use specimens which had lain for a very long time in spirit 

 so weak that the muscles and the connective tissue could be 

 removed fairly easily by preparation, whereby T avoided the 

 effect of the potash in making the thin chitin too transparent. 



These observations are here made in case any one should 

 wish to test or dispute my results, while at the same time I 

 emphatically urge those who are interested in the subject to 

 investigate in the manner indicated a larger series of forms 

 belonging to several orders. Inducements for a test may 

 possibly be afforded by ray chief results, which are as 

 follows : — The demonstration of three segments in the axis 

 of the appendages of Crustacea as the primitive and still 

 frequently existing condition ; the division of the Malaco- 

 straca, based inter alia upon the different structure of the 

 thoracic limbs ; the demonstration of the existence in the 

 case of Thysanura and certain Orthoptera of four pairs of 

 month-parts, with which those of the Amphipoda are homo- 

 logous ; and the proof of a much greater agreement between 

 the head of a ]\fachilis and that of the malacostracous 

 Crustacea than was hitherto assumed to be the case. 



It would lead us too far afield to quote (not to speak of 

 discussing) the enormous literature which belongs to the 

 questions here indicated. Only once or twice do 1 refer to 

 an author more precisely, when I have not found an oppor- 

 tunity of closely investigating the forms which are the 

 subjects of liis statements or am entirely ignorant of them ; 

 when, as most frequently happens, I content myself with 

 giving the name of an author in parenthesis, it signifies that 

 the writer in question has expressed the same opinion before 

 Vie (thus affording a confirmation of my statement), hut that I 



