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XIV. On some points in the Anatomy of the immature 

 Csenis macrura of Stephens. By A. E. Eaton, 

 B.A. 



[ Eead 6th July, 1868. ] 



The following observations are intended merely as a sup- 

 plement to tlie researches of other anatomists^ and do not 

 touch upon any details in the organization of Ccenis, 

 besides those which have been the subjects of their studies 

 in other genera of the Ephemeridoe ', neither do I purpose 

 reiterating the lines of investigation pursued by them in 

 connection with this particular genus. 



In the mature Egg, the germinal matter is segregated 

 at one end in such a way as to assume the appearance of 

 a somewhat lunate protuberance from it. * One might 

 liken its outline to that of the seed of the horse-bean, 

 with the expansion of the funiculus attached to it. This 

 seemingly appendant condition of the germinal matter is 

 not peculiar to this genus. In Ephemerella, Walsh^ the 

 mass in question constitutes nearly two-fifths of the egg, 

 from the rest of which it is marked out by a slight con- 

 striction ; but its form differs from that of the corres- 

 ponding part in Ccenis, in being sub-conical, instead of 

 crescent- shaped. Mr. Haliday, also, represents the 

 mature egg of Phloeothrips pini, Hal., with a small 

 appendix at one end (Walk. Brit. Mus. Cat. Homoptera, 

 part iv. pi. viii. fig. 15) . 



During its later suhaqueoiis stages of developm^ent (which 

 I have recently discovered) Ccenis resides in the beds of 

 rivers and streamlets, either near the surface of mud- 

 banks, or under stones, according to the nature of the 

 bottom. When it is dropped into water, it presently 

 begins to swim slowly, remarkably slowly for an Ephe- 

 merid, by means of the vertical movements of the body 

 usual in these insects, aided by feeble strokes with its 

 sprawling legs. 



The body is more than ordinarily pubescent ; in some 



parts it is even hirsute. The head, in what I regard as 



the immature C. halter ata. Fab., is armed with three 



rather short, obtuse, conical spines in the place of the 



ocelli; but in the type it is unarmed. The inner two 



divisions of the labium, are obtusely ovate ; the outer 



two are narrower, and somewhat curved : they are 



* Compare with this the yolk of an Osseous Fish's egg, — say Gasteros- 

 teus, as represented in Journ. Anat. & Physiol, vol. I. pi. xi. 1. g. c. 



TRANS. ENT. SOC. 1868. PART III. (SEPTEMBER). 



