240 
Argm persicus 
a lotig time that they consisted of uric acid or nrates. Pagenstecher^ 
was the first to apply a chemical test with the object of establishing 
their constitution, and concluded that they were composed of uric acid. 
Kersey^ is cited b}^ Bonnet® as having identified their substance with 
guanin, a discovery which has since been confirmed by Bonnet. 
Before leaving tbe subject of the Malpighian tubules, it should be 
observed that these structures in ticks are, in all probability, not 
homologous with those of the Malpighian tubules of the Antennata. 
In the latter class, the Malpighian tubules arise as invaginations of the 
wall of the proctodoeum, while in all Arachnida in which the subject has 
been investigated, they are derived from the mesenteron. The earliest 
reference to the subject, with which we are acquainted, is that of 
Loman'* (cited by Warburton®), who showed that in spiders the 
Malpighian tubules <)pen into the mid-gut and not into the rectum 
(hind-gut), and there is reason to believe that structures homologous 
with the Malpighian tubules of Insects are absent in the Arachnida, 
where their place is takeir by the coxal glands, which are considered to 
be the true excretory organs. 
Lankester®, in discussing the same subject, cites Laurie'^, who fouird 
the Malpighian tubules of Scorpions are developed from the mesenteron 
and are, therefore, hypohlastic in origin, while in the Hexapoda, they 
are derived from the proctodoeum and are epihlastic in origin. On 
p. 20.5 of the same work, Lankester cites Korschelt and Heider®, who 
point out that the hinder portion of the gut frequently acts in Arthro- 
poda as an organ of nitrogenous excretion, in the absence of any special 
excretory tubules, and that the production of such coeca from its surface, 
in separate lines of descent, does not involve any elaborate or unlikely 
process of growth. Lankester sums up—“In other words, the Mal¬ 
pighian tubes of the terrestrial Arachnida are homoplastic with those 
of the Hexap)oda and Myi'iapoda, and not homogenetic with them.” 
The Anal Canal and Anns. 
PI. XV, an.\ PL XVI, fig. 6 , an.', PI. XVII, fig. 4, an. ap., an. can. 
The anal canal is a very short wide laterally compressed tube which 
passes directly downwards from the ventral surface of the rectal sac to 
the anus, the upper opening of the tube being situated a short distance 
' Pagenstecher, H. A. (1861), p. 34. ^ Kersey (1872). 
® Bonnet, A. (1907), p. 87. Loman, J. C. C. (1885-87). 
5 Warburton, C. (1909), p. 331. “ Lankester, E. E. (1904), pp. 204-205. 
^ Laurie, M. (1890). s Korschelt, G. and Heider, K. (1892). 
