732 



SCIENCE. 



[Vol. II., No. 44. 



jfex,,.. 



enamel-oi'gau of the other, vertebrates, and 

 originate in the same waj'. So far, at least, 

 the lamprej' does not show an essentially dif- 

 ferent tj-pe of tooth-development from that 

 known in other groups. 



The cells of the ' enamel-organ ' are rapidly 

 proliferating, and have thrown off from their 

 outer surface a conical cap of cells {2d i.), 

 which are flattened, and which show an incip- 

 ient formation of pigment among them. This 

 hollow cone of cells is the rudiment of the 

 youngest tooth, which in the stage here de- 

 scribed is the second of the series. Outside 

 of the rudimentarj' tooth is a cone of jjolygo- 

 nal epiblastic cells, several layers deep (i.e.) ; 

 and this is again followed by the first tooth, 

 now almost completely cornifled and pigmented, 

 so that traces of cel- 

 lular structure are 

 but faintl}' discerni- 

 ble {1st t.). The 

 tip of this tooth has 

 just penetrated the 

 skin of the mouth, 

 and is elsewhere cov- 

 ered bj' the man}'- 

 layered epiblast (e. 

 m.). 



We see, therefore, 

 that the essential 

 parts of the tj'pical 

 1 ' ,• ,,_ vertebrate tooth are 



v-,r/vi- V,- " ^''"' 'i6i'^ present; name- 



^^^ ' '"™" ly, the mesoblastic 



Section through inDci- side of lip papilla, and the 

 of metamoiphofeing Igmprey. ^ ^ , . ., , 



«.m., epiblast of mouth; js(«., ovcr-hang epiblastic 



oldest tooth; 2(2 t, youngest pmrnpl-nvo-.qn 'Rnt 

 tooth; f.o., enamel organ; i.e., euamei-Olgan. XiUt 

 intermediate epiblast-cells be- the Ol'dinar}' tvpe of 



„=.^ =„„„„,..„ . „„ , ,„ „ (jgijijjj development 

 is here greatl3' modi- 

 fied. The papilla is never ossified ; and the 

 enamel-organ secretes no enamel, but func- 

 tions as a sort of tooth-gland, throwing off 

 successive hollow cones of flattened and cor- 

 nifled epiblastic cells. The actual tooth of the 

 lamprey is therefore not the homologue of 

 the entire tooth of a selachian, but simplj- of the 

 enamel-cap. It is not difficult, however, to 

 understand how the process seen in Petromj'zon 

 could be derived from that in the selachian. 

 In consequence of this change, another dif- 

 ference arises : as the papilla never ossifies or 

 becomes protruded, it is no longer necessary 

 that for every new tooth a new enamel-organ 

 should be formed bj' budding from the old one ; 

 so each enamel-organ is converted into a per- 

 manent tooth-gland, functional throughout the 

 life of tlie animal. 



tween Buccessive teeth; 

 oesoblastic papilla. 



This view of the peculiarities of dental devel- 

 opment in Petromyzon implies, of courje, that 

 this group of fishes was derived from ancestors 

 possessed of teeth of the ordinary or selachian 

 t3'pe. Further, as it is now very generallj' 

 admitted that teeth are only modified placoid* 

 scales, it follows that the lampreys are de- 

 scended, ultimately at least, from forms pro- 

 vided with placoid scales. 



Such a conclusion, however, does not hy any 

 means commit us to the view that the myxi- 

 noids are degenerate descendants of some gna- 

 thostomatous group, as this is no more implied 

 in the possession of ordinaiy calcareous teeth 

 than in the presence of the hornj' teeth which 

 the group has long been known to possess. 



W. B. Scott. 



NORDENSKIULD ON THE INLAND ICE 

 OF GREENLAND.^ 



In a series of letters to Mr. Oscar Dickson, Baron 

 Nordeiisl<i61d has given a detailed report of the lead- 

 ing incidents and results of his recent expedition, 

 though it will still be some time ere we can leam 

 what are the full gains to science. The leading 

 novelty of the expedition was, of course, the journey 

 into the interior of Greenland. 



After landing Dr. Nathorst and his party at Waigatz 

 Sound, Nordenskiold went back to Egedesminde, 

 which he reached on June 29. The following day he 

 left for Auleitsivik Fjord, from which the expedi- 

 tion was to start. He then proceeds : — 



On July 1 the Sophia anchored in the bay. We 

 found here a splendid harbor with clay bottom, some 

 seven fathoms deep, surrounded by gneiss rocks from 

 six hundred to a thousand feet in heiglit, the sides 

 of which are in some places covered with low but 

 close shrubs, or clothed with some species of willow, 

 mosses, and lichen, which, when we arrived, were 

 ornamented with a quantity of magnificent blossoms. 

 From one of the slopes a torrent descended, the 

 temperature of which was 12.3° C. The weather was 

 fine, the sky cloudless, and the air very dry. July 1 

 to 3 were employed in making preparations for the 

 ice-journey, while the naturalists made excursions 

 to variotts places in order to collect objects relating to 

 the conditions of the country. On the night of the 

 3d every thing was ready for a start; and, after some 

 difficulty in reaching the spot where the baggage was, 

 we were fairly off. The spot from ^\hich we set out 

 on the journey was only five kilometres from the 

 actual shore, and situated below a little lake into 

 which a number of glacier rivers fell. We proceeded 

 up the river in a Berton boat, purchased in England. 

 Ou the night of the 4th we camped for the first time 

 on the ice. The expedition consisted of nine men 

 besides myself. After a great deal of hard work in 

 getting the sledges over the ice, which was here very 

 ' From Nature, Xov. 1 and 8. 



