22 Dr Oashell, The Origin of Vertebrates. [Nov. 25, 



observation that the branchial cartilages are the first to be formed 

 in the Ammoccetes. We may then argue that in the direct 

 ancestor of the Vertebrate two axial lines of cartilage ought to be 

 found and from them a series of branchial bars should issue, which 

 bars should lie external to the branchise. We ought in fact to 

 find a cartilaginous skeleton exactly of the kind which exists in 

 Limulus ; where the two axial cartilaginous bars are found in the 

 two entapophysial cartilaginous ligaments of Ray Lankester and 

 the cartilaginous branchial bars are found in the cartilaginous rods 

 which spring from each entapophysis into each branchial appendage 

 as described by Gegenbauer. This is the only true cartilaginous 

 skeleton of Limulus, for the ento-chondrite is not cartilaginous but 

 is made up of tendon and muscle like the central tendon of the 

 diaphragm (as shown by Schimkewitsch); it stains also like tendon 

 and not like cartilage. 



Again, tracing back the histology of the skeletal tissues we see 

 how bone is formed from cartilage, and that cartilage is by no 

 means always quite the same in structure. Among the different 

 kinds we find that the branchial cartilages of Aminoccetes are 

 quite distinct and different to any found in the higher Ver- 

 tebrates. Further in Ammoccetes there is in addition to these 

 cartilages a peculiar fibro-massive tissue, from which according to 

 Schneider the cartilages arise, called by him muco-cartilage 

 (Schleim-knoiyel or Vor-Knorpel). This tissue-like cartilage gives 

 a characteristic deep purple stain with thionin. It shows its 

 ancestral importance by disappearing entirely at transformation, 

 being either converted into cartilage or invaded by blood and con- 

 verted into an areolar fat tissue. 



I conclude then that the immediate ancestor of the Vertebrate 

 possessed branchial cartilages of the structure of those of Ammo- 

 ccetes, which themselves arose from muco-cartilage. In other words 

 we are again led directly to the branchial cartilages and enta- 

 pophysial ligaments of Limulus, for their structure is word for word 

 the same as that of the branchial cartilages of Ammoccetes, they 

 stain in the same way with thionin, and the cartilage arises from a 

 fibro-massive tissue which resembles absolutely both histologically 

 and in its staining deep purple with thionin the muco-cartilage of 

 Ammoccetes. This muco-cartilage of Limulus is formed from cells 

 of the chitinogenous layer belonging to the entapophyses, so that 

 we see not only how the direct agreement of the cartilaginous 

 skeleton of Limulus with that of Ammoccetes both topographically 

 and histologically points to the identity of these two skeletal 

 systems, but also how we thereby obtain striking evidence of the 

 manner in whicli the chitinous skeleton of the Invertebrate gave 

 origin to the cartilaginous skeleton of the Vertebrate. 



