132 WALTER GARSTANG, M.A. 



Branchial apparatus. — A portion of the inner face of the pharyn- 

 geal wall is shown on PL V. fig. 4. The horizontal vessels form 

 three complete series and a rudimentary growth. The primary 

 vessels (h. v. 1), which give off branches* to the body-walls, are 

 usually of greater diameter than those of the remaining series. 

 Between each pair of primaries are situated one secondary vessel 

 (h. v. 2), and two tertiary vessels (h. v. 3), at approximately equal 

 distances. 



Connecting ducts (c. d.) arise from all these vessels and support 

 delicate internal longitudinal bars (i. I. b.) which are surmounted at 

 the points of junction by moderately stout conical papillae (p.) and 

 at intermediate points by comparatively slender ones (*'. p.). The 

 connecting ducts themselves are sub-triangular in shape when seen in 

 profile. The horizontal and internal longitudinal vessels delimit 

 meshes, which are sometimes almost twice as long as broad, and contain 

 four or five stigmata each. The stigmata are elongated, with rounded 

 ends ; they are frequently double, and then consist of an anterior and 

 a posterior portion of elliptical shape. The pharyngeal wall is minutely 

 plicated in a longitudinal direction. The meshes almost invariably 

 show some traces of a division into two equal portions by the formation 

 of an incomplete quaternary series of horizontal vessels ; the extent to 

 which this process is carried out varies in different individuals and in 

 different parts of the same pharynx. The process is interesting, and 

 may be completely traced in fig. 4. A small projection arises from the 

 internal face of an interstigmatic bar, at its middle point (see fig. 4, 

 upper row, third mesh from the left), and is joined by a similar 

 projection from the opposite wall of the stigma (see the mesh below). 

 The concrescence of the two projections forms a horizontal bridge across 

 the middle of the stigma. The formation of several such bridges 

 across adjacent stigmata thus gives rise to a small horizontal vessel 

 (see the mesh below), which may be said to form part of a quaternary 

 series ; these quaternary vessels (h. v. 4) may even form connections 

 with the internal longitudinal bars beneath the intermediate papillse 

 (i. p.) of those structures. My figure represents the condition of the 

 branchial apparatus in the individual shown in fig. 3 ; but in a some- 



* The origin of these branches — the dermato-branchial connectives — is 

 marked in some specimens by white spots upon the primary horizontal bars. 



