1914] Litile: Ocelli of Pohjorchis 321 



eye-spots, are not being added, since very small buds were found 

 in the largest specimens measured. Tentacles only 2 mm. long 

 were found to contain a small eye-spot. 



Compared with other naked-eyed Medusae, Pohjorchis presents 

 many points both of similarity and contrast. All have the eye- 

 spots located on or near the base of the tentacles and usually on 

 the upper side, though, as mentioned above, Lizzia is an excep- 

 tion to this rule. Whenever the eyes are borne on the lower or 

 inner side of the tentacles, the latter are carried upward at the 

 protective rim. The eyes may be arranged around the margin, 

 as in Pohjorchis, or in bunches to correspond with the bunches of 

 tentacles, as in Hippocrene. 



In the lens type of eye the sensory epithelium, pigment cells 

 alternating with sensory cells, and bipolar or multipolar nerve 

 cells, are found in every case, though the form and general 

 arrangement of cells may vary, as in the case of the sense cells 

 of Codonium princeps which are long, bottle-shaped cells with 

 a knob-like swelling near their outer ends. 



Pigmentation without the lens structure is found in such 

 forms as Syncoryne, Oceania, Corymopsis, Turris, and Bougain- 

 vilUa. The eye-spot may be either a simple collection of pigment 

 in the ectoderm or a more highly developed organ through the 

 presence of a light-refracting body. 



Transmitted May 3, 191S. 



BIBLIOGRAPHY 



Agassiz, a. 



1862. "Classification of the Hydroidae" in "Contributions to the 

 natural history of the United States of America" (1862), 

 4, 336-372. 

 1865. North American Acalephae. Illustrated catalogue of the Mus. 

 Comparative Zoology at Harvard College, 2, Mem. Mus. Comp. 

 Zool. Harvard College, 2, No. 2, pp. 118-121, 130-134, figs. 

 179-183, 202-214. 

 Agassiz, L. 



1849. Contributions to the natural history of the Acalephae of 

 North America. Pt. I. On the naked-eyed medusae of the 

 shores of Massachusetts in their perfect state of develop- 

 ment. Mem. Amer. Acad. Arts and Science, N. S., 4, pp. 

 221-312, pis. 1-8. 



