254 Transactions of the 



II. — On the Development of the Face in the Sturgeon (Accipenser 



sturio). By W. K. Parkee, F.R.S. 



{Bead before the Royal Mickoscopjcal Society, May 7, 1873.) 



Plate XX. 



Very remarkable protrusible mouths are to be seen amongst ordi- 

 nary Osseous Fishes, such as the Dory (Zeus faher), and in the 

 species known as Epibulus insidiator* But the Sturgeon belongs 

 to another "Order" — the "Ganoids" — and is, indeed, one of the 

 group farthest from the Osseous Fishes : forms of Ganoids that 

 come much nearer to our ordinary Fishes are to be found in the 

 North American lakes, namely, the Bony Garpike (Lepidosteus) ; 

 and in the Polypterus of the Nile. 



Yet the mechanism of the mouth and tongue of the Sturgeon 

 comes much nearer to that seen in Osseous Fishes than to the 

 curious Embryonic mouth of the Skate and Shark (" Elasmo- 

 branchii"). But in the latter group, in the Ganoids and also in the 

 Osseous Fishes (" Teleostei "), the arch of the mandible is loosened 

 from the skull, is confluent with the ptery go-palatine arch, and is 

 swung on the front of the lower end of a huge pier, which forms 

 part of the broken-up arch of the tongue. In some Fishes, as the 

 Pipe-fish (Fistularia), and the Hippocampus and its allies, this 

 pier is of enormous length, and the double arch carried at its 

 extremity is very short; so that while a mouth of this kind is 

 capable of great extension forwards on its hyoid hinge, it is itself 

 very small indeed. Those who have looked at the Sturgeon's head 

 will remember that it has a transverse, inferior, thick-lipped mouth, 

 which can be drawn downwards as a short, highly-arched tube : 

 the Fish is a ground-feeder ; and its mouth is very effective for the 

 purposes of its possessor. 



The proper skull of the Sturgeon is a huge mass of solid, 

 hyaline cartilage, covered, externally, by large ganoid, bony plates ; 

 behind it has the fore-end of the large, persistent notochord 

 entering it, and has several of its unossified vertebrae coalesced with 

 it behind. 



Nothing could have thrown any certain light upon the morpho- 

 logical meaning of the parts of the Sturgeon's face, except the 

 study of development; as this has not been possible in the early 



DESCRIPTION OF PLATE XX. 



Fig. 1. — Side view of facial arches of a young sturgeon — one foot long. 

 „ 2. — Lower view of the mouth-roof of ditto. 

 „ 3. — Inner view of mandible of ditto. 

 „ 4. —Section of lower part of stylo-hyal with cerato-hyal attached, of ditto. 



All these four figures are magnified. 

 „ 5. — Side view of palate and mandible of an adult sturgeon. 



* See Owen, 'Lect. Comp. Anat.,' vol. ii., p. 103, Fig. 37. 



