Trof. Nicholson — Progress in Palceontology. 5 



briefest manner. The first point in this connexion which demands 

 our attention is tlie immense benefit which has resulted to paleeon- 

 tology from the introduction of the microscope as an absolutely 

 indispensable instrument of palseontological research. The old 

 " macroscopic " method of investigation, as the Germans have 

 happily termed it, has been definitely abandoned ; and no 

 palaeontologist would now, except under special circumstances, 

 describe any doubtful or problematical Invertebrate fossil without 

 previously having subjected it to a rigid examination by means 

 of the microscope, at any rate in all cases in which his speci- 

 mens would allow of this mode of examination. It is impossible, 

 indeed, to exaggerate the immensely increased powers of observation 

 and description which palceontologists have acquired by the practice 

 of making transparent sections of fossils, suitable for microscopic 

 examination. Already, the results of this method of inquiry have 

 proved extremely important, and when its adoption has become more 

 universal, we may expect an even more remarkable increase of our 

 knowledge as to the intimate structure of many extinct forms of life, 

 which are at present but very imperfectly understood. 



Few departments of Invertebrate Palaeontology have shown the 

 beneficial effects of the introduction of the microscope into pal^onto- 

 logical investigations moi-e strikingly than is exemplified by the 

 Protozoa. I could not adduce a better instance of this than is afforded 

 by the remarkable and beautiful series of fossil sponges, which have 

 been generally grouped together under the name of VentricxdilidcB. 

 Though well known by their remarkable external configuration, and 

 unhesitatingly classified in accordance with this character alone into 

 genera and species, we had until lately really very little genuine 

 knowledge as to the structure and afiixiities of these old types of life. 

 They were originally regarded either as horny or as primitively 

 calcareoixs sponges, which had undergone silicification ; and it was 

 upon this view that D'Orbigny, Fromentel, and other observers re- 

 garded them as a special group, to which the name of Fetrosponffiadce 

 was given. We know now, however, that the VentricuUtidce, and a 

 number of other equally interesting and beautiful groups of fossil 

 sponges, dating from the Lower Silurian, are true siliceous sponges, 

 belonging to the same great section as the exquisite Venus' Flower- 

 basket and Bird's-nest Sponges [Euplectella, Soltenia, etc.) and 

 other SilicispongicB of recent seas, or, in other words, to such now 

 thoroughly established divisions as the Hexactinellidce and Lithistidce. 

 While referring to this subject, it is hardly out of place to notice 

 the remarkable conclusions which have been reached by Zittel 

 and Sollas as to the condition of fossilization of these sponges, 

 since these conclusions materially affect our ideas as to the general 

 process of fossilization, and as to the mode of preservation of the 

 sponges and allied organisms in particular. We are all familiar 

 with what is termed the " silicification " of fossils. We know 

 that it is a very common thing to find organisms in certain strata 

 in a " silicified " condition. In other words, we know that 

 fossils which we can assert positively to have been originally cal- 



