458 



PSYCHE. 



[May 1S93. 



different insects. In some cases, as in 

 the Coleoptera and Hymenoptera 

 (Doryphora, Chalicodoma), they are 

 budded off from the hind-gut when the 

 latter is still very shallow and the 

 embryo comparatively young. In other 

 cases they arise late in development 

 after the hind-gut has reached a con- 

 siderable length (Orthoptera : Blatta, 

 Xiphidium, etc). Notwithstanding 

 these variations, the derivation of the 

 hind-gut and its appendages from the 

 ectoderm is so easily ascertained that 

 it cannot escape even a very careless 

 observer.* 



The few accounts concerning the 

 origin of the Malpighian vessels in 

 Myriopoda are quite definite. Accord- 

 ing to Heathcotef in Jidus terrestris 

 a single pair of vessels is formed as 

 outgrowths from the hind-gut, and 

 Metschnikoffj long ago made a similar 

 observation on Strongylosotna gueri- 

 nii. Zograffs'§ figures show conclu- 

 sively that the Malpighian vessels of 

 Geophilus form no exception to the 

 general rule. It is, therefore, quite 

 certain that the Myriopoda and Hexa- 

 poda, which I propose to unite under 



* According to Graber (Vergleichende studien, etc. 

 Denkschr. d. k. akad. d. wiss. bd. 56, 18S9, p. 25 et 

 seq.) , the hind-gut probably arises from the mesentoderm 

 in Musca. This if true would make the Malpighian ves- 

 sels mesentodermic. I have elsewhere pointed out 

 (Psyche, June 1S91 , p. 98) what appears to me to be the 

 true explanation of the phenomena observed by Graber. 



fThe early development of Julus terrestris. Quart, 

 journ. micr. sci., vol. 26, 1886, p. 461. 



% Embryologie der doppelttiissigen Myriapoden. 

 Zeitschr. f. wiss. zool. bd. 24, 1874, p. 262. 



§ Material k moznania embrionalnavo razvetia Geo- 

 philus fermgineus Lk. e G. proxmius L. K. Trudi 

 zool. mus. Moscow, 1882. 



the term Eutracheata, agree in the 

 mode of origin of the excretory organs. 

 These may therefore be regarded as 

 strictly homologous in the two groups. 



Far less satisfactory are the accounts 

 concerning the so-called Malpighian ves- 

 sels of other Arthropods. Among the 

 Crustacea (Amphipoda) two, (or in 

 Melita only one) tubular diverticula of 

 the mid-gut have been called Malpigh- 

 ian vessels, on account of their resem- 

 blance in form and function to the 

 excretory organs of the Eutracheata. 

 But there is this great difference : the 

 Crustacean vessels are not derived from 

 the ectoderm but according to Spencer* 

 and Mme. Pereyaslawzewa,f from the 

 entoderm. 



Peripatus, I need hardly state, has 

 no Malpighian vessels, the numerous 

 pairs of nephridia subserving the excre- 

 tory function. 



In the Arachnida a pair of branching 

 tubules opening into the mid-gut near 

 its junction with the hind-gut have been 

 called Malpighian vessels. There are, 

 however, reasons for doubting their 

 homology with the urinary organs of 

 insects. Lomanj" believes that they 

 correspond to the mid-gut diverticula of 

 the Arthrostraca and maintains that they 

 do not contain urates. The accounts 

 of their origin in the embryo are con- 



*The urinary organs of Amphipoda. Q_. journ. micr. 

 sc. (2) v. 25, 1S85, p. 183-190. 



t Etudes sur le de'veloppement des Amphipodes. 1. 

 Le d^veloppement de Gammarus poecilurus , Rhk. Bull, 

 soc. imp. nat. d. Moscou, no. 2 ann£e 188S. 



X Ueber die morphologische bedeutung der sogenann- 

 ten Malpighischen gefasse der echten spinnen. Tij- 

 dschr. nederl. dierk. 5 deel. 1, 1S87. 



