538 H. H. SWTNNERTON. 



to the symplectic (McMnrricli, 83, p. G31). A transitional 

 stage between that exhibited by the stickleback and that 

 found in the salmon, trout, and even also in Amia (fig. 61), 

 occurs in such a type as Zoarces (Text fig. 3). These facts 

 seem to point to a process of reduction, going on within the 

 teleostean series as we pass from lowly to more specialised 

 types. In the stickleback the metapterygoid process lies 

 for its whole length on the symplectic, with its extremity 

 inclined somewhat to the inside and situated on a level with 

 the attachment of the stylohyal. 



The pala.tine process {qu. fia.) is also attenuated, but in 

 this respect it resembles the condition found in the salmon. 

 In stickleback and pipefish, owing to the forward position 

 of the mouth, this process is very short. Its exti'emity is 

 now connected with the ethmoid by means of an insignificant 

 tract of pro-cartilage. Though this connection is established, 

 there is no sign of any part of the process having arisen 

 independently, but chondrification has taken place from the 

 quadrate outwards. Stohr has said of the salmon that "der 

 pterygopalatintheil is demnach ein Auswuchs des Quadrat- 

 knorpels " (83, p. 11). The same is equally true of the 

 stickleback. In Syngnathus, McMurrich (83) has described 

 an independent cartilage, which he calls the ethmopalatine, 

 attached to the ethmoid in front and sepai\ated by a tract of 

 connective tissue from the " pterygoid process " of the quad- 

 rate behind. The same element is present in Siphonostoma 

 at all the later stages I have examined, viz. in individuals 

 varying from 14 mm. to 26 mm. in length, but it is joined to 

 the upper end of the rod-like quadrate by a tract of pro- 

 cartilage which apparently never becomes choudrified. 



Particular interest attaches to the relationship of the 

 extremity of the palatine process to the ethmoid. To fully 

 appi'eciate this it is necessary here to briefly describe this as 

 it is found in the' larval Amia and pike of a slightly later 

 stage. 



In Amia (PL 31, fig. 60), as in the salmon and trout, the 

 extremity of the palatine process is expanded, but it differs 



