190 
W. BALDWIN SPENCER. 
from regarding them as strictly homologous with the Mal- 
pighian tubes of Tracheata. 
EXPLANATION OF PLATE XIII. 
Illustrating Mr. W. B. Spencer's paper on “ The Urinary 
Organs of Amphipoda.” 
List of Letters employed. 
An. Anus. Cr. Concretions in urinary tubes. Cr 1 . Concretions which 
have passed from the tubes out into the hind gut. G. Genital organs. H. 
Heart. H. g. Hind gut. L. Liver tubes. Lo. Opening of liver tubes into 
mid gut. M. g. Mid gut. Mes. Mesenteries supporting and surrounding the 
various organs. M. Ig. Longitudinal muscular fibres of hind gut. M. tr. 
Transverse muscular fibres of hind gut. Muse. Ordinary muscles of the body. 
N. Nerve cord. R. Rectum. Sg. Last segment of the body removed 
with the gut. Ur. Urinary tubes. Ur 1 . Distal part of urinary tube, 
which is always bent forward. Ur. o. Opening of urinary tubes into gut. 
X. Point at which hind gut ends and mid gut begins. Y. Anterior termina- 
tion of mid gut. 
Pig. 1. — Part of alimentary canal of Talitrus locusta, removed from 
the body with the tail segment still attached. Only the mid and hind guts are 
present and the liver tubes, only one of which is shaded, the rest being only 
drawn in outline are turned forwards. The two urinary tubes are seen arising 
from the posterior end of the mid gut ; they have been pulled away from the 
side of the hind gut, close to which they lie naturally ; the constantly bent 
distal part lies normally in the last segment. Large and small concretions are 
seen filling up the tubes, some having passed out into the gut. 
Pig. 2. — Transverse section through hinder part of body of Talitrus 
locusta. The hind gut has a distinct cuticular lining beset with small points. 
Both urinary tubes are seen in section, each enclosed by a supporting mesen- 
tery, as is also the gut. Below the latter the nerve cord is seen in section. 
Fig. 3. — Transverse section through hinder part of Gammarus pulex. 
The plane of the section is oblique, so that the opening of only one urinary 
organ into the mid gut is seen ; the cells of the other one are also cut through, 
