NOTES ON THE TENOUS SYSTEM OF lURDS. 581 



to the ever increasing numbers of these parasites that tlie size 

 of the individuals composing the incoming generations of Aurelia 

 continued to become more and more diminutive. I shall, however, 

 attend to all these points more closely next j^ear, after which 1 

 shall doubtless be able to speak with more certainty regarding 

 them. 



Notes on the Venous System of Birds. 

 By Chables H. Wade, FJj.S. 



[Bead April 6, 1876.] 



I PROPOSE in the present paper briefly to draw attention to cer- 

 tain structural features in the anatomy of some birds. I cannot 

 claim that my discoveries are original, except in so far as they 

 were made without knowledge of previous work done in the same 

 field by other observers ; but, as I hope to show, the points of 

 which I shall particularly treat are so important, and have ob- 

 tained so little recognition hitherto, that no apology seems neces- 

 sary for introducing them to the notice of this Society. 



My interest in this subject was first excited a few weeks ao-o 

 when, in dissecting a specimen of a common Tomtit (the Marsh- 

 Titmouse, Parus palustris) I was surprised to find present, as it 

 appeared, only one jugular vein, the right. A second specimen 

 showed a like deviation from the normal type ; and, noting this, I 

 made a regular excursion through the well-known text-books, in 

 the hope they might contain some explanation which had before 

 escaped my reading. I may briefly detail the results of my 

 search, 



Owen contents himself with saying (Anatomy of Vertebrates, 

 ii. 203), " The vein of the right side exceeds the otlier in size; it 

 is often twice as large." To what considerable extent the state- 

 ment needs modifying I will show directly. 



Milne-Edwards says (Lemons sur la Physiologie &.c,, vol. iii. 

 p. 466) "The jugular veins are placed superficially on the sides of 

 the neck ; sometimes they are (both) of pretty nearly the same 

 calibre ; but in general that of the left side remains very attenu- 

 ated, while that of the right side presents a considerable volume." 



Gregenbaur, who seems closely to have followed Milne-Edwards, 

 says (I quote from the French translation by Car) Vogt, p. 80t), 

 " there is atrophy of one of the jugular veins (the left) ; it is bv 



38* 



