URINARY ORGANS OF THE AMPHIPODA. 
185 
considerable detail, and their works will be referred to in the 
descriptions which follow. 
The presence of these tubes in Gammarus was described by 
Sars, who, judging apparently from their position only, came to 
the conclusion that they were outgrowths of the hind gut, and 
analogous to the Malpighian tubes of insects. In both young 
and old specimens of Gammarus their existence may be demon- 
strated either by simple dissection or best by cutting continuous 
sections through the whole animal. Even in very young Gam- 
mari, which have just left the brood pouch of their mother, they 
form prominent objects. Thus, in one of 2 mm. length they arise 
in the third segment from the posterior end and pass forwards, 
lying dorsad of the alimentary canal through four segments, 
growing to a slightly greater length in the adult. 
To observe their structure and position with regard to the 
other organs, the best method, as before said, is to cut sections 
through the whole body. Fig. 3 represents one near the 
posterior end cut somewhat obliquely, so that only the actual 
opening of one of the tubes into the alimentary canal is seen. 
It will be observed that the epithelium lining both tubes and 
canal is similar and continuous, and that the former arise quite 
separately from each other on the dorsal surface. 
Below the canal the four liver tubes are seen cut in section, 
and below these again the nerve cord with ganglion cells on its 
ventral, and fibres on its dorsal side. 
A more anterior section shows that the two tubes lie closely 
side by side, each surrounded, as are the liver crnca, by a definite 
membrane, whilst the alimentary canal is supported by a well- 
marked mesentery which in this part divides the body cavity 
into two halves, a dorsal and a ventral. 
If a fresh specimen be taken the two tubes are seen to have 
their walls composed of long cells rounded internally (i. e. the 
end of each cell projects slightly into the lumen of the tube), 
whilst externally they are roughly hexagonal in shape. When 
stained they show large nuclei lying always on their outer side. 
The tubes pass forward, retaining the same position, until 
having traversed five segments they end blindly. 
