6 W. BALDWIN SPENCEE. 



Papillae. — These structuresj varying somewhat in number 

 and arrangement, appear to be constant features in the anatomy 

 of the Pentastomidse. Their presence has been described in all 

 forms save P. protelis, in which Hoyle was unable to find 

 them, though there can be little doubt that he would have 

 detected them had his material been in a better state of pre- 

 servation. Even in well-preserved specimens they vary remark- 

 ably in distinctness. 



The papillae can be clearly divided into two sets, which may 

 for convenience be described as («) primary and [b) secondary. 



(a) Primary Papillae (figs. 2 and 5). — These comprise 

 only two, and each of these forms a more or less prominent 

 elevation, lying a slight distance anteriorly to the depression 

 which holds one of the hooks placed nearest the mouth — that 

 is, one of the more posterior of the two pairs of hooks. In the 

 retracted state these papillae are scarcely noticeable, but at 

 other times they project markedly from the surface. Each 

 has, close to its apex, a minute opening, which serves as one of 

 the openings for the duct running forwards from the hook- 

 glands to be afterwards described. Though invisible in surface 

 view, each papilla bears one or more simple sense-organs placed 

 close to the opening of the duct. 



These papillae are the " Tastpapillen " of Leuckart, and were 

 regarded by him as the homologues of antennae. Lohrmann 

 states that the head-gland ( = hook-gland mentioned above) 

 opens upon them ; and Stiles, rejecting Leuckart's suggestion 

 of their homology with antennae, agrees with him in regarding 

 them as sense-papillse, and says that the head-gland opens to 

 the ventral side of the papillae. The anatomy of P. tereti- 

 usculum shows that we are dealing with a form in which we 

 find combined the features described singly by Lohrmann and 

 Stiles. The latter says, " Auf grund meiner Beobachtung 

 betrachte ich diese Papillen gleich Leuckart als Sinnespapilleu, 

 fiude jedoch keine Veranlassung sie als rudimentiire Anteunen 

 anzusehen." As will be shown soon, and as Stiles has already 

 pointed out in the case of P. proboscideum, sense-papillae 

 are present, related in position to the external pair of hooks, as 



