938 DR. A. HOPEWELL-SMITH AND DR. H. W. MARETT TIMS ON 



precede it. Spherules of calco-globuliii are clearly seen in many 

 of the ameloblasts. 



(iv) The abundant evidence of blood-vessels within the enamel 

 organ is a very striking feature (PL XLYII. fig. 5). The fact of 

 the vasculaiity of the enamel organ is one upon which there 

 are contradictory statements. Wedl, Magitot, Legros, Sudduth 

 and Paul deny the existence of blood-vessels in this situation. 

 On the other hand, Prof, Poulton and the late Prof. G, B. Howes 

 have mentioned their presence in the enamel organs of the Rat. 



In Macropus there is no dovibt Avhatever. They can be seen 

 entering the enamel organ apparently at more than one point on 

 the surface, and are often of sufficient size to clearly recognise the 

 blood corpuscles within them. They can be traced to a point about 

 midway between the outer and inner enamel epithelium, but we 

 have not seen them pi^oceeding farther, neither have we found them 

 in the stratum intermedium, the position in which they wei-e 

 described by the avithors above mentioned. 



The fact of the vascularity of the enamel organ is one of im- 

 portance in connection with the various theories held as to the 

 processes of the calcification and enamel formation and of the 

 functions of the stellate reticulum. It is extremely probable that 

 the unusual vascularity of the enamel organs in this animal is 

 correlated with the precocious development of the enamel, to which 

 reference has just been made. 



(v) Evidence of the fusion of enamel organs. There appears to 

 be some evidence of the possibility of the occurrence of such fusion 

 though the evidence is not decisive. PI. XLYIL fig. 4, shows the 

 subdivision of an enamel organ into two parts by an epithelial 

 septum passing fi-om the outer enamel epithelium to the inner 

 where the latter lies over the apex of the dentinal papilla. This 

 occurs in more than one cheek-tooth and maybe seen on both sides. 

 We have never met with anything of the kind before. That this 

 septum is not a small capillary running directly across the stellate 

 reticulum we are assvired. We can offer no other suggestion than 

 that it is a double enamel organ taking part in the formation of a 

 single tooth. 



This is a point of considerable morphological importance as 

 bearing upon the question of the evolution of the molar patterns. 

 Fusion is presupposed to have occurred bj' all writers who believe 

 in any form of concrescence, but little satisfactory evidence has 

 been forthcoming in the mammalia and little weight can be given 

 to the evidence derived from the disintegiation of the Cetacean 

 molars. 



Amongst the lower vertebrates the evidences of fusion seem to 

 be conclusive. In one family of upper Palfeozoic Sharks, the 

 Cochliodontidse, there is a fusion into plates not only of adjoining 

 teeth of one series, but also of successional teeth of several series. 

 Semon (4) has also shown that a fusion of individual cusps takes 

 place in CercUodiis, and Rose has seen the cusps in the process of 

 fusion in the teeth of a chameleon (3). Woodward [loc. cit.) speaks 



