Vhylogcny of the Arachnida. 293 



to the rectal vesicle, with which both glands subsequently 

 become connected, I cannot express an altogether dertnite 

 oj)inion ; but the origin of the glands themselves is quite 

 beyond doubt, as I have shown distinctly by means of figures 

 in my Kussian paper (No. GO, tig. 52 &c.). With reference 

 to the development of the (Malpighian) excretory tubes in 

 the other Arachnids, we only possess observations upon 

 Scorpions and Aranea?. In the first place it was shown by 

 Kowalewsky and Schulgin (No. iio, p. 46) in the case of 

 Avdroctonus oryiatus that the end-gut is invaginated only to 

 tlie length of the penultimate caudal segment, after which the 

 origin of the Malpighian tubes as outgrowths of the mid-gut 

 at a time when the end-gut was still quite solitl was described 

 by Laurie in Euscorpiiis italicus (No. o9, p. 128). These 

 two papers com})lete one another, and since the end-gut of 

 the Scorpion is very short, and in the first stages of develop- 

 ment is distinctly separated from the mid-gut, it seems to me 

 that by means of these memoirs the endodermal origin of the 

 excretory organs is demonstrated with sufficient clearness. 



The observations as to the development of the Malpighian 

 tubes in Armeffi are, as is well known, very contradictory. 

 Altogether this question has been touched upon by Barrois 

 (No. 3), Balfour (No. 1), Locy (No. 40), Schimkewitsch 

 (No. 59), Morin (No. 48), and Kischinouye (No. 29). 

 Balfour, who is followed by Schimkewitsch and ]\Iorin, con- 

 siders that these organs arise from evaginations of the end- 

 gut : Balfour's description (No. 1) is very short ; early stages 

 in the development of the jMal])ighian tubes he did not 

 observe. The other two investigators, however, diflTer from 

 one another in details — a fact which, as it seems to me, 

 deserves attention, and is due either to the difference between 

 the species observed {Lycosa, Tlirridion, and Pholcus) or to 

 insufficient accuracy in the observations themselves. Schim- 

 kewitsch describes in Lycosa saccata (No. 59, p. 562) a 

 longitudinal division of the blind end of the proctodeal 

 invagination into an upper portion, which develops further 

 into the cloacal sac (rectal vesicle), and a lower section, the 

 actual rectum, which subsequently sends out two cell- 

 ])rocesst's, that are originally solid and constitute the first 

 rudiments ot the Malpighian tubes. V\ ith reference to 

 Thtridion maculatian, it is stated by Morin {loc. cit. pp. 161- 

 162) that the blind extremity of the end-gut expands and 

 becomes the cloacal sac, into which " the ends ot the Mal- 

 jiighian tubes open ; " the author in question expresses 

 himself more distinctly with regard to Pholcus phalaiujuides 

 ([). 193) : " on both sides," he writes, " of the ^ poche stereo- 



