) 
83 
flowing posteriorly, and the others into the currents 
passing to the base of the mouth. 
The main currents are easily seen by placing the living 
animal on its back, in a drop of sea water on a slide. then 
covering with a thin cover glass and examining with a 
tin. objective. 
The blood currents described above do not continue to 
flow for any length of time in the one direction. At one 
period they may be flowing as indicated by the arrows in 
Plate II., fig. 2. Then they suddenly slacken and reverse, 
and stream for a time in exactly the opposite course. 
Sometimes the blood corpuscles are seen to simply oscillate 
backwards and forwards, making no advance, but at other 
times they pass rapidly along in a definite manner. 
There are no independent organs of respiration. It has 
been suggested by Hartog and others that the blood is 
probably aerated from the sea water contained in the thin- 
walled alimentary canal by the method of “anal respira- 
tion,” which has been described in Cyclops, Caliqus, 
Argulus, Daphnia, Cypris and other lower Crustacea. 
The cuticular exoskeleton over the surface of the body 
is in most places so thick that the respiratory change of 
gases may be supposed to take place much more readily 
through the very thin layer of chitin which lines the 
rectum. There are dilator muscles attached to the wall 
close to the anus, and the peristaltic movements of the 
whole alimentary canal may aid in the production of 
inhalent and exhalent currents of water. It appears, 
however, to the present author that further precise obser- 
vations are required to substantiate this hypothesis. 
No organ corresponding to the “shell gland” described 
in. various lower crustacea, and shown by Claus, Hartog 
and others to be a renal organ, has been found. 
