622 MR. E. B. POULTON ON THE [DcC. 18, 



organ, and hence the series (figs, xiv— xviii. Plate LIV.) in which 

 the most protected forms show independent evidence of their primitive 

 condition. With the most perfect protection, there is also the 

 presence of bulbs over the whole of the papillary surface ; and as the 

 papilla becomes less protected, the bulbs gradually sink into their 

 normal position of a zone round the papillary base. Even in the 

 highest marsupial papillae there is some trace of the original pro- 

 tection in the presence of a much constricted base. In some mar- 

 supial tongues botli conditions coexist, and the less protected, 

 radially symmetrical form is the posterior {i. e. the papilla most 

 sheltered by its position, and thus able most quickly to abandon the 

 old excessive protection). It has been much in favour of this theory 

 that I have been able — in more than one part of the subject — to 

 confirm previous suggestions by subsequent work. 



As to the primitive triangle of circumvallate papillae, I have no 

 doubt that we have here the ancestral form of the inverted Y arrange- 

 ment in many higher animals (e. g. man). It is possible that, the 

 above being the history of the primitive circumvallate papillae, in 

 some cases their number may be added to by direct development 

 from fungiform papillae ; but this is only a suggestion founded on a 

 superficial examination. 



EXPLANATION OF PLATES LIV. & LV. 



Fig, I. Natural size. Tbe back part of the tongue of Hahnaturus tialahatus seen 

 from tlie right side. Tbe upper surface is seen to be densely papillate, 

 the papillae being of the coronate type {i. e. papillaa surmounted by a 

 circle of fine, liair-like, generally recurved, secondary papillfe, the whole 

 of mechanical functifm, and as far as is yet known peculiar to and 

 always present in Marsupials ; see fig. xxviii, Plate LV.). /.^>. Fungi- 

 form papilla of the normal sti'ucture ; few in number and scattered 

 irregularly among the coronate papilLx' above the lateral line of junc- 

 tion with tbe non-papillate surlace. I. f. p. Lateral filiform j)apillae, 

 forming the limits of the papillate surface at the posterior part of the 

 jvuiclion with the non-papillate surface. These large and probably 

 tactile papilloB are very constant in this position in the tongues of 

 Marsupials and probably of other Mammalia. The lateral gustatory 

 organ, when present, is to be found (as in this tongue) in the non- 

 papillate surface just below the anterior part of the row of filiform 

 papilla. I. g. 0. Lateral gustatory organ, here presenting the appear- 

 ance of a row of circular elevations with a crater-like depression 

 (generally somewhat elongated) on the summit of each ; beneath 

 these elevations is a longer, less regular row of smaller but otherwise 

 apparently similar elevations, gld. d ; the depressions on the sum- 

 mits of these latter are gland-duct? leading from glands of mucous 

 type. No taste-bulbs are to be found in the walls of the ducts, but 

 they are present in small numbers in those of the larger elevations 

 {I. g. 0.). But in other respects these last depressions are precisely 

 similar to the former ; they lead into glands of serous type, and all 

 their relations are those of gland-ducts (see fig. xxxi. Plate LV.). We 

 therefore have here the simplest form of lateral organ — a row of 

 simple gland-ducts, in the walls of which scattered bulbs are developed. 

 From this type we can pass by gradual stages to the complex lateral 

 organ of Rodents, in which there is but little indication of the true origin, 

 except when looked at in the light derived from the study of such a 

 tongue as that of Hcdinaturus. The arrow ( 3= - ) in all cases points 



