May 1 893. J 



PS re HE. 



459 



flicting and somewhat unsatisfactory. 

 In the scorpion according to Laurie* 

 the vessels arise as tubular outgrowths 

 of the mid-gut. Derivation from the 

 ectoderm is in this instance precluded, 

 since the hind-gut, or proctodaeum, 

 does not make its appeai'ance till after 

 the Malpighian vessels have arisen. 

 On the other hand Morin,f Schimke- 

 witchj and Locy§ are of the opinion 

 that the vessels in the Araneina are 

 budded oft' from the distal end of the 

 hind-gut in much the same manner as 

 in insects. The only remaining possi- 

 bility ; viz., the derivation of the Mal- 

 pighian vessels from the mesoderm is 

 advocated by Kishinouye.|| 



These wide differences in opinion 

 regarding the origin of the Malpighian 

 vessels in all Arthropods, excepting the 

 Eutracheata, commend us in doubt- 

 ing the homology of the various or- 

 gans hitherto comprised under the 

 same name. In default of definite 

 proof of entodermic origin in the ves- 

 sels of Crustacea and Arachnida, the 

 suggestion of a new terminology would, 

 of course, be premature. But even if 

 the organs in question should be ulti- 

 mately shown to be ectodermal in the 

 lower Arthropods, as well as in Eutra- 

 cheata, the few conclusions advanced 



*The embryology of a scorpion (Euscorpius italicus). 

 Q. journ. micr. sc. vol. 31, 1S90, p. 12S. 



f Zur entwicklungsgeschichte der spinnen. Biol- 

 centralbl. bd. 6, 1S87. 



X Etude sur le ddveloppment des araignees. Arch, 

 biol. tome 6, 1887. 



§ Observations on the development of Agelena tieevia. 

 Bull. mus. comp. zool. vol. 12, no. 3, 1S86. 



|| On the development of Araneina. Journ. coll. sci. 

 im. univ. Japan, v. 4, pt. i, 1S90. 



in the present paper will be in no wise 

 affected thereby, since I do not under- 

 take to establish the ancestral number 

 of Malpighian vessels for the Arthropoda 

 as a class but only for the subordinate 

 group Hexapoda. 



Both the peculiar numerical con- 

 stancy of the Malpighian vessels within 

 limited groups of Insecta, and the great 

 numerical disparity between different 

 groups, could not fail to attract the at- 

 tention of the entomotomist. Brauer,* 

 especially, has made use of these con- 

 ditions in his classification of insects as 

 Polynephria and Oligonephria. It was 

 also readily seen that the Malpighian 

 vessels when limited in number are, 

 with very rare exceptions, arranged in 

 pairs. Hence Gegenbaurf and others 

 have drawn the correct inference that 

 the paired arrangement represents a 

 primitive feature. It was furthermore 

 observed that embryos and larvae of 

 polynephric forms have a much smaller 

 number of vessels than the correspond- 

 ing imagines; the converse being very 

 rarely, if ever the case. When, within 

 more recent years, the great phylogen- 

 etic value of the embryonic stages was 

 established, it was readily surmised that 

 the condition of the excretory organs in 

 the embryo might furnish some clue to 

 their ancestral number and arrangement. 

 The interesting facts brought to light by 

 the study of the embryonic excretory 

 system of vertebrates certainly justify 



* Systematisch zoologische studien. Sitz.-ber. math, 

 naturwiss. klasse. k. akad. wiss. 91, bd. i.abth. Wien. 

 1885. 



f Grundriss der vergeescheinden anatomic 2. aurlage. 

 Leipzig, 1S7S, p. 292. 



