LEPTOMEDUS.E — OBELIA. 



245 



nearly at right angles to main stem. These side branches give rise to numerous polypites and 

 reproductive calycles. The longest side branches arise from about the middle regions of main 

 stem. The branches pursue a zigzag course, each internode trending at an angle of 45 from 

 previous one. The pedicels of the polypites arise from the internodes of the branches. They 

 are ringed at base and at distal end, and are usually about as long as the intervals between the 



128. 



Fig. 124. — Obelia rommissuralis, after A. Agassiz, in North American Acalephae. 



Fig. !2f. — Obelia diehotoma, after Hincks, in British Hydroid Zoophytes. 



Fig. 126. — Obelia "articulata" (=0. diehotoma), after A. Agassiz, in North American Acalcphx. 



Fig. 127. — Obelia dichotoma, after Hincks, in British Hydroid Zoophytes. 



Fig. 128. — Obelia piriformis, after A. Agassiz, in North American Acalephs. 



internodes of the branches. Each polypite has 24 to 30 long, slender tentacles. The mouth 

 is at the extremity of a prominent proboscis. The hydrotheca is about 1.5 times as long as 

 wide, and its upper edge is smooth and circular. The reproductive calycles are situated at 

 the bases of the pedicels of the polypites and also at the origins of the side branches from the 

 main stem. They are borne upon short, cylindrical stalks composed of 5 or 6 rings. The 

 calycle is slender and conical, tapering gradually from the proximal to the distal end where it 



