Franklin Dexter — 21 
an appreciable amount of coagulum. T[requently close to its wall, some 
spherical bodies are seen. ‘These vary much in size, as well as in num- 
ber. I have no notion whatever as to what they are. The triangular 
vesicle has been a very interesting puzzle to me, nor is it as yet solved. 
I call it a vesicle simply for the want of a better name. Tor a long time 
it did not seem possible that it was not a blood-vessel, or perhaps a 
lymph space, and to-day I am unable to explain it, so must leave the 
subject for future investigation. ‘There are, however, a few curious 
facts in regard to it. It is an inconstant structure. I have seen it in 
embryos from 60 mm. in length, up to young chickens after birth, but 
I have never been fortunate enough to meet it in an earlier or in a 
later stage. At times it is present, but I am inclined to believe that 
it is more frequently absent. When present it seems to be situated in 
about the same spot, and may be identified in either a sagittal or a 
frontal section. In the former it is apt to be somewhat oval (Fig. 5); 
and in the latter triangular in section (Fig. 7). 
In one series of the adult chicken, where the vesicle was absent, the 
blood-vessel (which appeared in Fig. 7 as a compressed vessel beneath 
it), was triangular in form, and presented precisely the same shape as 
this vesicle. As the vesicle begins to appear in serial sections the wall _ 
is first met, then one meets the cavity, and lastly a wall. Surely when 
one considers the structure of this object under the high power, it is 
difficult to conceive of its being either a lymph space or a blood-vessel, 
and after diligent search through many sections in several embryos, I 
have never been able to find a single blood corpuscle within its cavity, 
and as far as I know, its cavity does not communicate with that of the 
forebrain. 
Dendy (4), in a most admirable and interesting paper on Sphenodon, 
refers to what he calls an accessory vesicle situated between the tubules 
of the paraphysis and the parietal stalk. He describes it as sacculated, 
irregular in shape, containing no blood corpuscles, unconnected with 
the forebrain, and as disappearing at a moderately late stage of develop- 
ment. He does not believe it to be either a vessel or a lymph space. 
Moreover, as pictured in his article, the lining epithelium seems to be of 
quite a different character from the vesicle in question Burckhardt (1) 
mentions a vesicle in lacerta vivipara, which is close to the epiphysis, 
and could not, I should fancy, be confounded with this one. Under 
the head of “ Nebenorgan ” and “ Nebenscheitelorgan,” different kinds 
of vesicles have been described in different animals by various authors, 
but I fancy that they should all be associated with the epiphysis rather 
than with this vesicle, which certainly can have no connection with it. 
