138 Transactions of the Society. 



this entire room to overflowing ; nevertheless their separate struc- 

 tures, whether of bones, teeth, hairs, horns, feathers, or scales, as 

 well as their blood-corpuscles and various tissues, have doubtless 

 often attracted the investigation of our Fellows. I venture to think 

 that an introduction to these animals and their ancestors in past 

 times may not be so inappropriate as might at first sight appear, 

 and that some slight account of them, as a whole, may even 

 enhance the interest we may hereafter take in their minute struc- 

 tures when brought to our notice under the Microscope. 



From the earliest Archaean rocks up to the Carboniferous, 

 through a series of deposits more than fifteen miles in thickness, 

 comprising Cambrian, Ordovician, Silurian and Devonian forma- 

 tions, all are marine deposits, and in consequence yield scarcely 

 any trace of other than marine organic remains. 



The first appearance, then, of Vertebrate life upon our earth 

 must necessarily have been marine, or at least aquatic — in fact, in 

 the form of fishes only. 



The first fishes were, however, without hardened skeletons, 

 having a persistent notochoral, a condition of the spinal column 

 characteristic of the embryo of most vertebrate animals, but only 

 found to be persistent through life in the adult of a few groups of 

 Fishes and Amphibia. 



The First Vertebrates. — The lowliest of these (forming the 

 Leptocardii or Pharyngobranchii) is the " Lancelet " or Amphi- 

 oxus — a minute animal, flattened in body and pointed at both ends, 

 which has no hard parts whatever, only a membrano-cartilaginous 

 skeleton without vertebra?, ribs, or jaws. 



The mouth in Amphioxus is furnished with cirri ; respiration 

 is performed by gills enclosed in a branchial chamber ; and pul- 

 sating vascular trunks serve instead of a heart. 



Having no hard parts to be preserved in a fossil state, we of 

 course cannot claim for it great antiquity by reason of its remains 

 having been met with in Palaeozoic strata ; nevertheless, its wide 

 geographical distribution on the sandy coasts of the North Sea, of 

 the Mediterranean, of South America, of the Indian Ocean, and 

 other widely separated localities, justify us in considering it to be 

 a very ancient and primitive,* as it undoubtedly is a most simple, 

 form of vertebrate. 



In the next group (the Cyclostomi or Marsipobraxchii) are 

 placed certain cylindrical vermiform fishes, without pectoral or 

 pelvic fins, with a simple cartilaginous skeleton and persistent 

 notochord. Eespiration is performed by means of a series of six 



* On similar grounds Prof. E. B. Poultou claims for the curious Arthropod 

 Peripatus (which has not been found fossil, but has at present a most extensive 

 terrestrial geographical range) a geological antiquity greater thau any other form 

 of life we are acquainted with, " at least twice as remote as the earliest known 

 Cambrian fossil." Presidential Address (Zoology), British Association, Liverpool, 

 1896. 



