of the Fishery Board for Scotland, 



211 



VI.— NOTES ON SOME POINTS IN TELEOSTEAN DEVELOP- 

 MENT. By H. Chas. Williamson, M.A., B.Sc. (Plates VIII. 

 and IX.). 



The foUowiiif^ observations were made while I held the Exhibition 

 (1851) Scholarship of the University of St Andrews. The work was 

 carried on at the Zoological Station, Naples, and at the Gatty Marine 

 Laboratory, St Andrews. At Naples I was afforded the privilege of 

 occupying the table of the British Association. 



The Absorption of the Yolk, and the Primitive Circulation in 

 Pelagic Teleostean Ova. 



The process of the absorption of the yolk in Teleostean ova is not one 

 which has received much direct attention. In demersal eggs the absorp- 

 tion of the yolk is mainly effected by means of an elaborate vitelline blood 

 circulation. In pelagic ova, with one or two rare exceptions, no vitelline 

 blood circulation exists. The study of the subject involves an examination 

 almost solely of live eggs. 



I find that in those pelagic ova which I have been able to examine there 

 is a distinct, though very much modified, vitelline circulation. The 

 elements of this circulation are not, however, blood corpuscles but yolk 

 corpuscles. I have noticed this circulation in the ova of the following 

 twelve species, viz. : — Three species of the ova of Murcenid(B (Raffaele),* 

 Merluccius vulgaris, Engraulis encrasicholus, Species No. 3 {Cory- 

 phcena?) Raff., Gadus oeglefinus, Gadus merlangus, Pleuronectes itali- 

 cus{?), Pleuronectes flesus, Pleuronectes limanda, Clupea sprattus, 

 Uranoscopus scaber. In the case of the last-named species, I refer to a 

 stage previous to the appearance of the complete blood circulation. 



The corpuscles which form the elements of the circulation are simply 

 little portions of periblast. They are clear, transparent bodies of varying 

 size and shape. They are, for the most part, roughly spherical or oval 

 in form, and show no distinct bounding wall. They are merely little 

 naked portions of protoplasm. Before the heart is formed these corpuscles 

 are to be seen scattered over the periblast. When the heart begins, at 

 first slowly and feebly, to pulsate, the corpuscles begin to move over 

 the periblast towards it. (The venous end of the heart opens into the 

 interior of the yolk sac). Once free from the periblast they enter the 

 heart, and from it are pumped through the already formed vessels. These 

 consist in, two lateral arteries (b.v., figs. 1 and 15) — the forerunners of the 

 branchial veins — uniting to form the aorta, which runs posteriorly to a 

 point a little short of the tip of the tail; and the caudal vein (c.v., fig. 7), 

 which, arising near the tip of the tail, debouches into the posterior end 

 of the yolk sac. 



At first the number of corpuscles entering the heart from the yolk sac 

 is small, but, as development proceeds, the number increases gradually. 

 The inner surface of the yolk sac is lined with a layer of periblast, and 

 on it are to be seen numbers of corpuscles. In the embryo of the anchovy 



* Raffaele, " Uova qalleqqianti del Golfo di Napoli" Mittheil, Zool. Station, Neapel 

 Bd. 8. 1888. 



