1881.] Development of the Skull in Lepidosteus osseous. 107 



II. " On the Development of the Skull in Lepidosteus osseous." 

 By W. K. Parker, F.R.S. Eeceived November 3, 1881. 



(Abstract.) 



The materials for the present paper were kindly sent to me by 

 Professor A. Agassiz ; they were for the use of Mr. Balfour and 

 myself, and consisted of fifty-four small bottles of eggs and embryos 

 in various stages. These very valuable materials were obtained from 

 Black Lake by Mr. S. W. Garman and Professor Agassiz, and many 

 of the embryos were described and figured by the latter in the 

 " Proceedings of the American Academy of Arts and Sciences," 

 October 8, 1878. 



Having received from my friend the author a copy of his im- 

 portant paper, I at once wrote to ask permission to work his 

 materials out, thoroughly ; suggesting that Mr. Balfour would under- 

 take the embryological part of the work. 



On receipt of my letter Professor Agassiz kindly acceded to my 

 wish, and the results of our investigations are now ready for publi- 

 cation. 



Mr. Balfour's part of the work has been done with the assistance of 

 my son, Mr. W. N. Parker, and their joint labour will include the 

 anatomy of various organs of the adult fish. 



We have had additional materials from Professor Burt Gr. Wilder ; 

 these were larger young than those supplied by Professor Agassiz ; 

 Mr. Balfour also has obtained several adult fishes in spirit ; and I 

 am indebted to Professor Flower for an adult in the dry state. 



Finding that we were in a condition to do some useful research on. 

 this important Holostean Ganoid, I pressed Dr. Traquair to take up 

 the skull of the adult ; this he consented to do ; and I am daily ex- 

 pecting that his paper will be sent to the Royal Society. 



My observations on the skull and visceral arches have been made 

 on embryos and young, varying from one-third of an inch to 4^ inches 

 in length ; I have (artificially) divided these into six stages. Cartilage 

 was being formed in the smallest examined by me, but in my second 

 stage, embryos five-twelfths of an inch long, this tissue was quite 

 consistent, and I succeeded in dissecting out all the parts. The large 

 notochord at this stage bends downwards under the swelling hind- 

 brain, and then turns up a little at its free end ; passing into the 

 lower part of the fissure between the mid- and hind-brain, it reaches 

 beyond the middle of the cranium, and just touches the infnndibulum 

 and distinct pituitary body. 



The paired cartilages, " parachordals," that invest the notochord 

 only cleave to its hinder three-fifths ; these bands then diverge and 



