376 Reports and Proceedings — Royal Microscopical Society. 



I will now only venture to glance at some of the Invertebrata ; 

 leaving the Vertebrata to be discussed upon another occasion. 



"In the first place " (Mr. Crampton writes) "the lowly-organised 

 groups have persisted in spite of the gradual evolution of more and 

 more highly-organised forms, and this must be due in large measure 

 to their rapid growth and reproductive powers. 



" That groups appear to have a shorter range in time as they 

 acquire a higher degree of organisation. 



"That living forms of groups that are dominant at the present 

 time rarely show ancestors of such great specialisation as themselves. 



"That forms that are now isolated in their zoological affinities, and 

 bordering on extinction, are generally highly specialised in some 

 direction, but often show signs of degeneration, and usually have 

 ancestors of greater specialisation during some former period of 

 dominance. A few, at any rate, seem to show a smaller degree of 

 fertility than might be expected. 



" Other forms which have come down to us from a distant period 

 with small amount of change, or with very gradually-acquired 

 specialisation, often show a great power of resistance to death. 

 They are also generally extremely fertile. 



" That extinct groups seem almost invariably to have acquired 

 a great degree of specialisation during their period of dominance. 



"That the more specialised genera and species of groups tend to 

 have a shorter range in time than the less specialised, although they 

 frequently appear to have temporarily acquired a greater dominance. 



"When a group shows very quickly -acquired variation and 

 specialisation its range is usually very restricted. 



" That the later forms in extinct groups frequently show signs of 

 degeneration, and sometimes a more primitive organisation than the 

 most specialised forms, possibly owing their persistence to their 

 slower specialisation. 



" That long retention of primitive characteristics, or a great degree 

 of stability and want of variation, has been usually associated with 

 a long range in time. 



"That higher groups do not spring from the most specialised 

 forms of the parent groups before them in time, but from some 

 generalised form in those groups which had retained a more primi- 

 tive organisation." And, lastly, I would add — 



That those forms which have persisted through long past periods 

 of geological time, have also an extremely wide geographical dis- 

 tribution at the present day. As might naturally be expected, it is 

 the loivly-organised forms which show the longest geological history. 



I. Protozoa. — Eadiolaria are found throughout the whole geo- 

 logical series and are world-wide in their distribution. 



Of the Foraminifera about two-thirds out of 2,000 species occur 

 fossil. The longevity of some genera is truly remarkable, e.g., 

 Lagena, Nodosaria, Textularia. The first two range from Silurian, 

 and the last from Carboniferous times to the present day. Fnsidina 

 and Schwagerina are world-wide in their distribution in Carboniferous 

 time, forming entire beds of limestone. (They are, however, con- 

 fined to the Carboniferous.) 



