560 GEOLOGICAL SURVEY OF THE TERRITORIES. 



EXPLANATION OF PLATE XXIII. 



Artemia gracilis Verrill (from New Haven), details. 



Fig. 1. Artemia gracilis YerriW. Head, showing tlie relation of the brain to the eyes, 

 optic nerves, and ocellus (ocel), with the stomach and liver ; 7n(1, mandible ; 

 gl, rudimentary shell-gland. 



Fig. 2.. Front of the body, showing the circulation of the blood; hf, heart; the dots 

 and arrows indicate the course of the blood-currents ; int, intestine. 



Fig. 3. End of the same individual represented by Fig. 2 ; lit, end of the heart, with 

 the two valves (seen at Fig. 3a) ; rec, rectum ; m, three pairs of muscular 

 bands which hold the rectum in place. 



Fig. 4. Portion of the heart during action; the arrows on each side point towards 

 the ostia or valvular openings ; the blood discs are represented within 

 the heart itself ; ep,c, epithelial cells in the walls of the heart; m, muscles 

 which hold the heart in place. 



Fig. 5. End of the body ; rec, rectum; m, muscles; anus, vent. 



Fig. 6. One of the compound eyes; cone, one of the crystalline cones; retina, the 

 black retina; op. n, the optic nervnles; ojyn, the main optic nerve; r. 

 m, retractor muscle of the eye ; g. op, ganglion opticum, consisting of gang- 

 lionic cells, X i B. 



Fig. 7. Circulation of the blood in a foot, the dots representing the blood discs; the 

 arrows indicating the course of the blood. 

 Drawn from the living specimens, with the camera lucida. by the author. 



