294 Ilerr J. Wagner on the 



rale ' two ectodermal processes arise, which are the first 

 rudiments of the Malpighian tubes." The ditference between 

 the descriptions of the two authors deserves notice, because, to 

 judge from Schimkewitsch's figures (No. 59, pi. xxii. fig. 6 : 

 the requisite figures are not given by Morin), on their first 

 appearance the histological structure of the rectal vesicle is 

 not the same as that of the rectum. By Barrois (No. 3) 

 and Kisciiinonye (No. 29) the ]\lalpighian tubes of the 

 Arancje are derived from the mesoderm ; according to 

 Kiscliinouye the Malpighian tubes are outgrowths of the 

 rectal vesicle, which is of mesodermal origin. They are 

 originally solid, as is stated by Schirakewitsch ; the union of 

 the cloacal vesicle with the rectum occurs subsequently. 



Finally, according to Locy's observations (No. 40, p. 75) 

 the Malpighian tubes arise as outgrowths from the posterior 

 end (" pre-stercoral tube ") of the mid-gut. Unfortunately 

 Locy's description is not illustrated by figures; if, however, 

 we compare those of his sagittal sections that pass through 

 the hinder end of the mesenteron and the rectal vesicle 

 C stercoral pocket," figs. 55, 56, and 70) with Schimke- 

 witsch's figure alluded to above, Ave might suppose that, in 

 the description of the latter, the anterior portion of the 

 rectum, from which the Malpighian tubes develop, and in tliat 

 of the former the posterior end of the " pre-stercoral tube " are 

 identical. This posterior eiidodermal process seems to be of 

 interest because it corresponds to the hinder process in Ixodes 

 (No. 66, ]). 100) and to the caudal process of the mid-gut in 

 the Scorpion. 



It seems to me that, remembering the above-mentioned 

 resemblance between the descriptions of Schimkewitsch and 

 Kischinouye (namely the statement that the first rudiments 

 of the excretory tubes are solid), and, further, the remark 

 made by the latter to the eflfect that the proctodteum enters 

 into connexion with the rectal vesicle at a late stage, I can, 

 on the basis of ray own observations upon Ixodes, and after 

 comparing the same with what is known as to the Scorpion, 

 harmonize the different observations upon Araueae only to the 

 following extent : — In all Araneae the posterior process of 

 the mesenteron, which lies close to the rectal vesicle and 

 develops even before the endoderra grows round the yolk, is 

 more or less distinctly marked; in certain cases the Mal- 

 pighian tubes arise directly, as (at first compact) outgrowths 

 of the portion of the mesenteron alluded to ; in others the 

 two compact rudiments of the Malpighian tubes separate from 

 the posterior end of the mesenteron, which adjoins the rectal 

 vesicle, and fuse secondarily with the latter (as in the case of 



