762 



MICROSCOPIC PALEONTOLOGY. 



Fig. 406. 



593. It is obvious that, under ordinary circumstances, only the 

 hard parts of the bodies of Animals that have been entombed in 

 the depths of the earth are likely to be preserved ; but from these 

 a vast amount of information may be drawn ; and the inspection 

 of a Microscopic fragment will often reveal, with the utmost cer- 

 tainty, the entire nature of the organism of which it formed part. 

 In the examination of the minuter fossil Corals, and of those 

 Polyzoaries (§ 445) which are commonly ranked with them, the 

 assistance of the Microscope is indispensable. Minute fragments 

 of the Tests or Spines of Echinodermata, and of all such Mollus- 

 cous Shells as present distinct appearances of structure (this being 

 especially the case with the Brachiopoda, and with the families of 

 Lamellibranchiate Bivalves most nearly allied to them), may be 

 unerringly identified by its means, when the external form of these 

 fragments would give no assistance whatever. In the study of the 

 important ancient group of Trilobites, not only does a Microscopic 



examination of 

 the ' casts ' which 

 have been pre- 

 served of the sur- 

 face of their Eyes 

 (Fig. 406), serve 

 to show the entire 

 conformity in the 

 structure of these 

 organs to the 

 ' composite ' type 

 which is so re- 

 markable a cha- 

 racteristic of the higher Articulata (§ 516), but it also brings to 

 light certain peculiarities which help to determine the division 

 of the great Crustacean series with which this group has most 

 alliance.* 



594. It is in the case of the Teeth, the Bones, and the Dermal 

 skeleton of Vertebrated animals, however, that the value of 

 Microscopic inquiry becomes most apparent ; since the structure of 

 these presents so many characteristics that are subject to well 

 marked variations in their several Classes, Orders, and Families, 

 that a knowledge of these characters frequently enables the Micro- 

 scopist to determine the nature of even the most fragmentary 

 specimens, with a positiveness which must appear altogether mis- 

 placed to such as have not studied the evidence. It was in regard 

 to Teeth, that the possibility of such determinations was first 

 made clear by the laborious researches of Prof. Owen,+ and the 

 following may be given as examples of their value : — A Rock-f ornia- 



* See Prof. Burmeister "On the Organization of the Trilobites," pub- 

 lished by the Ray Society, p. 19. 

 1 See his magnificent "Odontography." 



Eye of Trilobite. 



