330 Mr. W. K. Parker on the Development of the [Feb. 13, 



Sir Wyville Thomson and Mr. H. N. Moseley; the latter (who made 

 the collection in the Island of Ascension), sending me the smaller 

 specimens, and the former the ripe, and nearly ripe yonng. 



Through the liberality and kindness of these gentlemen, I am pnt in 

 possession of an invaluable series of specimens, several dozens in number ; 

 the smallest being only half an inch long measured along its curve. 



Sir Wyville Thomson, having accepted my offer of the memoir I 

 am preparing on this type of reptile for the " Challenger " Series of 

 papers, I am anxious to lay before the Royal Society some at least of 

 the results which I have obtained ; so that there may be a connexion 

 kept up between my papers, and this slow ingathering of results be 

 garnered in known places, for the benefit of those who will sift and 

 use them. 



I have for many years been familiar with the existence of both 

 paired and unpaired elements in the spine and hinder part of the 

 skull : . and also with the three cartilages that build up the fore part of 

 the chondro-cranium. 



My attention, however, having been directed most to the symme- 

 trical jpro-chcrdal bands, — the middle and fore part of the trabecule 

 cranii, — the anterior azygous cartilage, although always before my 

 eyes, has never, until lately, received the attention it deserves. 



In my first paper (on the skull of the ostrich tribe) I held views 

 with regard to the trabeculoe which I hold now; but there has been 

 an intermediate period in which I have fallen into, what I must now 

 consider to be a serious error. 



This error lay in the placing, both by Professor Huxley and myself, 

 of the trabecule cranii in the category of visceral arches. 



Both of us have known for many years that the hinder part of the 

 trabeculse of the newt are para-chordal, and I more recently discovered 

 that the hinder part of the basi-cranial plate is developed separately 

 in the Amphibia. 



Professor Huxley restricts the term " para-chordal " to these hinder 

 plates ; I am satisfied that the term must have a wider application. 



Nevertheless, what the Selachians, and all types above the Ichthy- 

 opsida show, satisfies me that Rathke was right in considering the 

 trabecule to be mere continuations of the moieties of the basal plate 

 or "investing mass." 



I quite agree with Mr. Balfour in looking upon the whole of these 

 tracts, right and left, to be the undivided representatives of the paired 

 neural arches of the spinal region, where, as a rule, they are distinct 

 from each other, and are developed between the spinal nerves, being 

 inter-segmental. 



I am satisfied that dying out of the notochord in front does not 

 affect the real nature of the jpro-chordal tracts. 



Until I understood the development of the pituitary body, its rela- 



