NUNNELEY, ON THE RETINA. 227 
sheath of the choroid, as the corolla of a tubular-shaped 
flower is surrounded by its calyx, but that the sheath without 
colour in reality encloses the entire cone. That the cones 
are wanting in all reptiles except the chelonian. 
In birds Hannover considers bodies very different in form 
as the cones jumeaux (those which I have called conoidal or 
fusiform rods); because they are sometimes surmounted by 
two coloured globules and are surrounded by the rods. He 
states, as already mentioned, that the citrine-coloured 
globules are situated at the outer end of these cones.* In 
mammalia he describes the cones jumeaux as being shorter 
than the rods, with their external ends terminating in two 
short and abrupt points. 
Mr. Bowman was the first to describe the bulbs in the 
human retina. He says they are solitary, globular, or egg- 
shaped, transparent bodies, sometimes having a small blunt 
spur upon them, turned towards the choroid, placed at 
regular intervals amongst the rods, much less numerous than 
the rods, of larger size, but not so long, and sessile upon the 
granules. Unlike Hannover, who believes these bodies not 
to exist in reptiles except the chelonian, Mr. Bowman thinks 
they not only do exist, but that in the frog they are nearly 
as numerous as the rods. 
Hassall, in his description of the microscopic anatomy of 
the eye, makes no allusion to the existence of such bodies as 
cones or bulbs, which evidently he had not detected. 
KOlliker’s figures and descriptions of the cones are al- 
together at variance with those of both Hannover and. 
Bowman. He states that the cones are rods, which instead 
of a filament at their inner extremity, are furnished with a 
conical or pyriform body. That each cone consists of an 
external, thicker and longer finely granular extremity, more 
or less ventricose, and which passes into a common rod ; and. 
an inner, shorter portion, in which an elongated or pyriform, 
more opaque and brilliant body, is enclosed ; the cones being, 
like the rods, continued by fine filaments into the deeper 
layers of the retina. 
I have searched most carefully for these bodies in the eyes 
of many animals, but I cannot say that I have satisfied my- 
self of the existence of any bodies such as have been 
described in the perfectly fresh eyes of any creature, except 
* In the text Hannover states that the cones jumeaur are surmounted 
by. the citrine-coloured globules, while in his figures of these parts, and in 
the description of them, he represents the cones as surmounted by the 
ruby-coloured globules. (‘Recherchés microscopiques sur le Systéme 
nerveux. ) ; 
