CIRCULATION or THE BLOOD IN PYROSOMA. 275 



But if the flatter side of the lens be placed nearer the 

 object, then r = Q, and as the correction varies inversely as 

 the square of r or 36, the correction will be 36 times smaller 

 for the refractive index, and consequently = 0*0196 -f- 36 = 

 000054. A thickness of -rVth of an inch in this case only 

 changes the value of the refractive index calculated in this 

 way by a decimal in the fourth place. 



Here, 



Approximate value of |U = 1*61813 



Correction for -r'-,Tth thickness = 0'00054 



Corrected value of ju = 1*61759 



Or refractive index corrected = 1*6176 nearly. 



On the CiRCULATTON of the Blood in Pyrosoma, especially 

 as observed in the Embryto. By P. Payesi, Assistant 

 to the Professor of Comparative Anatomy in the Univer- 

 sity of Naples. (With Plate XII.) 



At the commencement of last winter I was occupied in 

 studying the very interesting phenomena of the alternating 

 current of circulation in the Salpaj, when several living ex- 

 amities of Pyrosoma (P. giganteum, Sav.), caught in the bay, 

 were brought to the Laboratory of Comparative Anatomy for 

 the researches on phosphorescence, which Professor Panceri 

 continues to prosecute with such important results. 



It is well known that M. Milne-Edwards was the first ^ to 

 announce that the Ascidians of this celebrated animal arc 

 l^rovided with a heart analogous to that of the other Tunicates, 

 and that it reverses similarly periodically the direction of its 

 movements. This discovery has been more recently con- 

 firmed by Professor Huxley ^ and by MM. Keferstein and 

 Ehlers.3 It Avas, therefore, natural that I should turn my 

 attention at once to this point, and since I have been fortu- 

 nate enough to discover some new facts with regard to it, 

 following the request of Professor Panceri and Dr. Krohn, of 



* " Sur la circulation du sang cliez les Pyrosomes," ' Anuales des So. 

 Nat.,' iii ser., t. xij ; ' Zoo!./ 1839 ; ' Comptes llendus,' t. x, 1840 ; 

 ' Institut.,' viii, aniiee vi, 321, 20 Fcviier, 1810; 'Observations sur les 

 Ascidies coinposees des cotes de la Manclie,' Paris, 1811, p. 13. 



- " Observations upon tbe Anatomy and Physiology of !>alpa and Pyro- 

 soma," ' Phil. Trans.,' 1851. 



•' ' Zoologisciic Beitiage,' Ncapcl n. Messina, 1861. 



VOL. XII. — iNEW SBK. U 



