Phyhgeny of the Arachnida. 293 



to the rectal vesicle, with which both glands subsequently 

 become connected, I cannot express an altogether definite 

 opinion ; but the origin of the glands themselves is quite 

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

 in my Russian paper (No. 66, fig. 52 &c.). With reference 

 to the development of the (Malpighian) excretory tubes in 

 the other Arachnids, we only possess observations upon 

 Scorpions and Aranese. In the first place it was shown by 

 Kowalewsky and Schulgin (No. 35, p. 46) in the case of 

 Androctonus ornatus that the end-gut is invaginated only to 

 the 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 solid was described 

 by Laurie in Euscorpius italicus (No. 39, p. 128). These 

 two papers complete 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 Aranea3 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). 

 13alfour, who is followed by Schimkewitsch and Morin, 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 Malpighian tubes he did not 

 observe. The other two investigators, however, differ 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, Theridion, 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- 

 processes, that are originally solid and constitute the first 

 rudiments of the Malpighian tubes. With reference to 

 Theridion maculatum^ 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 of the Mal- 

 pighian tubes open ; " the author in question expresses 

 himself more distinctly with regard to Pholcus phalangoides 

 (p. 193) : " on both sides," he writes, " of the '■ poche stereo- 



