34 Dr Gaskell, The Origin of Vertebrates. [Nov. 25, 



to get through even liquid food — , but also how with the increasing 

 brain development the great mass of liver and generative organ 

 was shifted from the cephalic to the abdominal region, thus bulging 

 out the ventral surface of the body until it came into contact with 

 and fused with the lamellar branchial appendages on each side. 

 In this way the great class of Arachnids was formed, but in 

 vain as far as further evolution went, for no amount of room 

 around the brain could prevent the constricting action of the 

 enlarged oesophageal commissures on the oesophagus. Still among 

 those Limulus and Scorpion-like forms which were in those days 

 lords of creation and amongst whom the struggle for existence was 

 very keen, there were some in which the ventral surface did not 

 reach up to and fuse with the lamellar appendages, although by the 

 coming together of these latter a body surface like that of Eurypterus 

 was formed. In these cases then a respiratory chamber was formed 

 with gills and gill slits between the fused appendages, then came 

 the piercing of the operculum so as to put this chamber into 

 communication with the oral cavity. Such opening of communi- 

 cation is preserved for us embryologically as the breaking through 

 of the septum of the stomatodaeum, for this septum is in the exact 

 position of the operculum and has nothing to do with the velar 

 appendages. In this way then these animals took in water of 

 respiration through the mouth or gill slits into a chamber formed 

 by the branchial appendages and with this respiratory water food 

 of various kinds was naturally taken. Such food could be digested 

 because as shewn by Miss Alcock the skin of Ammocoetes pours out 

 a secretion for the purpose of keeping its skin clean, which is easily 

 capable of digesting fibrin. It appears from Hardy's researches 

 that a similar secretion is poured out on the carapace of Daphnia 

 and other Crustaceans. With the growth of the lower lip or 

 metastoma and the modification of the basal portion of the last 

 locomotor appendage, which basal part was inside the lower lip, 

 into a valvular arrangement like the velum, the animal was able 

 to close the opening into the respiratory chamber and feed as 

 blood sucker in the way of the rest of its kind, or when food of the 

 kind was scarce, keep itself alive by the organic material taken 

 into its respiratory chamber with the muddy water in which it 

 lived. 



In this way then we see how little by little a chamber was formed 

 by the lamellar branchial appendages which functioned also as a 

 digestive chamber. 



Such I imagine to have been the origin of the respiratory 

 part of the vertebrate alimentary canal, and the manner of forma- 

 tion of the rest of the tube is shown to us by the evidence of 

 phylogeny, embryology and palaeontology. 



Tracing back the alimentary canal along the Vertebrates we 



