1894.] TADPOLE OF XENOPTTS L-ST^IS. 105 



trace of the tentacles. The tentacles in these tadpoles are in the 

 form of a small process of the body connected with it by a 

 narrower stalk ; it is covered with a layer of columnar epidermis, 

 and the interior is filled with a mass of dense tissue. It shows 

 no resemblance to the sucker in its minute structure. A narrow 

 rod of cartilage runs towards it from the ethmoid just above the 

 joint where Meckel's cartilage articulates, but does not reach it. 

 A slip of muscle is attached to the base of the rudimentary 

 tentacle. 



In a full-growTi or nearly fidl-grown tadpole such as that dis- 

 played in the accompanying coloured drawing (Plate XIII. fig. 4) the 

 tentacles are of considerable length, with a slender bar of cartilage 

 running right along them as is figured by Parker {loc. cit. 

 pi. Ivii. figs. 1, 2, &e.). They are inserted so exactly at the 

 angle of the mouth that they are deeply grooved by it. During 

 life a blood-stream can be observed to pass along the tentacles. 

 The histological structiu-e is not in any way remarkable. Beneath 

 the epidermis is a certain amount of pigment. The interior of the 

 tentacle is taken up bv a network of connecti^'e tissue. On that 

 side furthest away from the body arc two blood-channels lying 

 side by side ; the axis of cartilage is small relatively to the 

 diameter of the tentacle. Mr. Boulenger, in a footnote appended 

 to Mr. Leslie's paper quoted above, compares the tentacles to the 

 " balancers " of Triton and Amhli/stoma. This can hardly be, if 

 the latter are, as Mr. Orr states \ the homologues of the external 

 gills belonging to the mandibular arch. 



Mouth-cavity and Pharynx- — In the newly-hatched tadpole 

 (May 29) the mouth is only a depression not communicating with 

 the gut ; there are no gill-slits and no skull. On the following day 

 the mouth was established. The most important fact with regard 

 to the mouth-cavity has already been established by Parker and 

 Leslie ; that is, of course, the entire absence of the horny larval 

 teeth. To confirm the absence of these characteristic structures 

 by microscopical sections is not, perhaps, an altogether unneces- 

 sary piece of work. At no stage in the development of the 

 tadpole of this frog did I succeed in discovering the least trace of 

 the structures in question. 



In tadpoles of May 31 some of the characteristic features of the 

 mouth-cavity and pharynx are already obvious. 



Just behind Meckel's cartilage is a deep recess of the mouth- 

 cavity ventral in position ; laterally this becomes a narrow slit, 

 close to the cartilage, and appears to be the first visceral cleft, 

 though I have not found any connection with the exterior. It 

 differs from the succeeding visceral clefts in being directed more 

 forwards, their inclination being at right angles with the longi- 

 tudinal axis or oblique in the opposite direction. The first 

 branchial cleft lying behind the hyoid arch is deep and narrow. 

 It is at right angles to the longitudinal axis, whereas the succeeding 



^ " Notes on the Development of Ampliibians, &c.," Q. J. M. S. 1889, p. 295. 



