ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 167 



urate or urates, the extract evaporated to dryness, tlie residue extracted 

 with boiling absolute alcohol and this extraction twice repeated, the 

 alcoholic solution poured away, the residue again boiled in distilled water 

 and filtered while hot. To the filtrate an excess of acetic acid was added, 

 and after the lapse of some hours crystals were easily found with a 1/5 

 in. objective. These occur mostly in hexahedral plates, also in the so- 

 called " coffin-shaped " crystals and in prismatic needles crossing each 

 other, also in groups of star-shaped form composed of prismatic and 

 " whetstone " crystals, and in other forms. 



Some of the residue, when evaporated to dryness and nitric acid was 

 added, effervesced ; on evaporating the acid the residue was reddish. On 

 holding a glass rod wet with ammonia close to it, a fine purple colour 

 was seen, and on adding caustic soda instead of ammonia it showed a 

 beautiful violet colour. 



On applying the same methods to the contents of the nephridium of 

 Helix aspersa a similar result was obtained, the crystals, however differing 

 in shape and size, but corresponding, nevertheless, to the well-known 

 forms in which uric acid is known to crystallize. Some of the crystals 

 obtained were cubical, some hexahedral, others prismatic with truncated 

 angles, others coffin-shaped, and so on. Both in the case of Periplaneta 

 and Helia; the size of the crystals depends on the method of preparation ; 

 for instance, they are smaller when the acetic acid solution is boiled. 



The dried residue in the case of Helix also gave the murexide reaction 

 distinctly, and the above-mentioned colour changes with caustic potash. 



From the nephridium of Limax Jiavus similar crystals were obtained, 

 and in. this case too the murexide reaction was equally well marked. 



In the juice of the nephridium of Helix spherical crystals are found, 

 which have been mistaken by some observers for crystals of the colouring 

 matter of the so-called bile of this mollusc ; they probably consist of 

 urate of soda (and calcium), and are at all events the urate of the base 

 which yields uric acid by the above treatment. In their interior needles 

 can be seen radiating from the centre to the periphery. It has been shown 

 by Griffiths that the "green gland" of the crayfish can be made to yield 

 crystals of uric acid, and he has more recently found uric acid in the organ 

 of Bojanus of Anodon, but in his experiments caustic potash was used ; a 

 method open to the objection that possibly, though not probably, the 

 reagent may have had something to do with the result ; but in the present 

 case acetic acid was the only reagent used, which is not open to this objec- 

 tion. 



Hence it may be safely concluded that the view held that the Mal- 

 pighian tubes of insects and the nephridium of the Palmonate Mollusca 

 function like the kidney of vertebrates is quite correct. 



(4) Cutting-, including' Imbedding and Microtomes. 



Water-bath Apparatus for Paraffin.* — Mr. E. L. Mark finds it pre- 

 ferable to have a water-bath for each student instead of a common tank for 

 all, a plan which has the advantage of all the materials being close at 

 hand. Moreover, it is more convenient to have the top of the bath nearly 

 level with the top of the table, rather than as a tripod standing on the table. 

 The gas-jet should be adjustable for distance in preference to the bath. 



The bath (fig. 25) is a modification of that used at the Naples Zoological 

 Station. It is fixed on a wrought-iron bracket to the end of the w<jrk- 



* Amer. Natural., xx. (1886) pp. 910-4 (3 fig?.). 



