184 
W. BALDWIN SPENCER. 
At the suggestion of Professor Moseley, to whom I am 
indebted for advice and the material necessary for the work, I 
have investigated these organs in two or three typical forms, 
and have, moreover, attempted in the following article to give 
a short summary of what appears to be known concerning their 
existence and nature in the various specimens in which they 
are found. 
Within the Crustacea they are apparently confined to the 
Edriophthalmata, whilst even amongst these their range is 
limited as they are not known to exist in the Isopoda. I have 
cut continuous transverse sections through the marine from 
Idothea, the fresh-water Asellus, and the terrestrial Oniscus, 
but in none of these are there present any appendages opening 
into the hinder part of the alimentary canal. In the Amphi- 
poda and in Caprella, on the other hand, there is no difficulty 
in demonstrating their existence. 
Of English authors, Huxley , 1 whilst treating of the Edrioph- 
thalmata, merely says, “ Occasionally there are one or two caeca 
which open into the posterior part of the intestine and appear 
to be urinary organs analogous to the Malpighian caeca of 
insects.” 
Gegenbaur 2 , speaking of the appendages of the hind gut in 
Arthropoda, says, “ In the Crustacea we sometimes meet with 
caecal organs on the hind gut, as, for example, in the larvae of 
the Copepoda, but we cannot safely form any opinion as to their 
significance,” whilst he makes no mention of the organs in 
Amphipoda. 
Balfour , 3 also in his summary of arthropodan development, 
says, “ The derivation of the Malpighian bodies from the proc- 
todaeum is common to most Tracheata. Such diverticula of the 
proctodaeum are not found in Crustacea.” These particular 
appendages, as well as the manner of their development, are 
unnoticed by him. 
Various foreign investigators have dealt with the subject in 
1 * Anatomy of Invertebrated Animals,’ p. 364. 
2 ‘ Elements of Comparative Anatomy,’ English translation, p. 276. 
3 * Comp. Embryology,’ vol. i, p. 452. 
