296 HeiT J. Wagner on the 



Arachnids and other Tracheata. The Malpighlan tubes of 

 Insects have frequently been studied, and their function is 

 known to us more thoroughly than that of the Malpighian 

 tubes in the Arachnids, with reference to which we possess 

 only isolated observations. Without submitting the subject 

 to a more minute investigation, I will confine myself to 

 certain statements in literature. 



According to Schindler (No. 60, p. 588) the existence of 

 uric acid in the Malpighian tubes of Insects was demon- 

 strated first by Keller, and afterwards by Leuckart ; Schindler 

 himself has proved the presence of the ordinary urates (urate 

 of soda and ammonia) in these vessels. Kowalewsky has 

 recently shown (Nos. 32 and 33), by means of a series of 

 experiments upon various Insects, that their Malpighian tubes 

 distinctly excrete indigo-carmine (indigo-sulphate of soda) 

 introduced into the body-cavity, and possess a distinctly 

 perceptible alkaline reaction (for the effect upon litmus, vide 

 No. 32, pp. 65-66) . A precisely similar energetic behaviour 

 towards indigo-carmine has also been discovered by Kowa- 

 lewsky in the case of Myriopods (No. 33, p. 205). If we 

 now turn to the Malpighian tubes of Arachnids, this is what 

 we find : — According to the observations of Plateau (No. 52, 

 p. 530), with whom Loman (No. 41) concurs, neither free 

 uric acid nor the typical urates occur in the Malpighian tubes 

 of Spiders *. Kowalewsky, by whom the behaviour of the 

 Malpighian tubes of Insects and Myriopods with regard to 

 indigo-carmine has been so distinctly demonstrated, makes 

 similar statements only with reference to the Araneaj (No. 34, 

 p. 203) t, in which, however, the liver plays the chief part in 

 the excretion of the indigo-carmine ; as to the Malpighian 

 tubes of /Scorpio and Soh/uga, Kowalewsky is silent ; in the 

 Scorpion, on the other hand (and partly also in Solifuga), the 

 tubular portion of the coxal gland has a function similar to 

 that of the Malpighian tubes of Insects. The liver of the 

 Scorpion, contrary to that of the Araneas, has an acid reaction, 

 as in the case of Crustacea. " This reaction of the liver," 

 says Kowalewsky (No. 34, p. 204), "in conjunction with 

 the presence of a kidney {i. e. the coxal gland), which con- 

 sists of a vesicle and the urinary duct, still further confirms 



* Bertkau'8 statement (No. 9) contradicting this is refuted by Loman. 

 In Ixodes the Malpighian tubes and the rectal vesicle are tilled with 

 sphere-crystals, which are regarded by M^guin (No. 43) as an alkaline 

 salt of uric acid ; uric acid and its salts have similarly been described 

 by Nalepa (No. 50, p. 204) in the Malpighian tubes of Tyroglyphus. 



t He studied chiefly Lycosa Latreilli and Eucharia castanea. 



