264 EF, RAY LANKESTER, 
side of the true mouth within the przoral atrium or open 
continuation of the epipleura, which forms the oral hood 
or upper lip of Amphioxus. They do not communicate 
with the lymph-spaces in the two latero-ventral folds as 
J. Miller supposed, but they lead into the anterior angles 
of the pharynx, perforating the septum which divides pre- 
oral from postoral atrium. ‘They thus correspond exactly 
in their relations to other parts with the hyoidean slit of 
the young Petromyzon Planeri, to which Prof. Huxley has 
drawn attention in the comparison of the heads of Petro- 
myzon and Amphioxus (‘ Proc. Roy. Soc.,’ Jan., 1875). The 
existence of these hyoidean apertures in Amphioxus tends 
to confirm the truth of the views which he has expressed as 
to the agreement of various parts in the two animals. 
Preoral atrium and true mouth, or pharyngeal orifice.— 
At present, in the absence of drawings, I will merely point 
out that the so-called buccal cavity is formed by the forward 
continuation of the two lateral growths (epipleura) svhich 
form the side-walls of the atrial chamber. These atrial 
parietes or epipleura at their anterior termination remain 
disunited in the middle line ; but, nevertheless, on account 
of its homology, we may speak of the unclosed space as 
well as of the closed one by the common name ‘ atrium.’ 
The preoral atrium is lined by a membrane dotted with 
brown pigment, exactly as is the postoral atrium and the two 
pigmented epithelia are (according to Kowalewsky) develop- 
mentally continuous. Posteriorly, this oral cavity is closed 
by an obliquely-placed inflection of its walls. In the lower 
part of this obliquely-directed wall is a small orifice facing 
downwards and forwards, and surrounded by a very thick 
and powerful sphincter muscle. This orifice (which appears 
to be the original mouth) leads by a short passage upwards 
and backwards through the thickness of the sphincter 
muscle into the capacious pharynx, which above extends 
forward beyond the vertical plane of the pharyngeal orifice. 
The pharyngeal orifice and sphincter, when that portion of 
the pharynx is removed and looked at in the horizontal 
position from the oral side, has the appearance of a solid 
circular mass with a conical central depression narrowing to 
a fine passage. On each side, forming the angles of the 
pharynx, are seen the duct-like connections of that organ 
with the hyoidean slits or pores. 
Structure of the Notochord.—I am able to confirm Dr. 
R. Kossmann (‘Verhandl. der Wiirzburger Phys. Med. 
Gesellschaft,’ Neue Folge, vol. vi) as to the existence of a 
series of stellate cells in the upper median line of the noto- 
