VAS DEFERENS— VIREO 1013 



(p. 139, Fig. 1, X.). Lymphatics and lacteals unite, and generally 

 follow the course of the bigger arteries and veins, often surrounding 

 them with anastomosing network. The lymph vessels of the tail 

 and hinder parts of the body enter the hypogastric veins, and at 

 the point of junction a small contractile "lymph-heart" is regularly 

 developed in the embryo and persists in many forms until maturity. 

 The lymphatic vessels of the trunk and intestines chiefly accompany 

 tlie aorta descendeiis and the mesenteric and coeliac arteries, finally 

 opening into the two superior venfB cavx, as also do the branches of 

 the lymphatic stems that come down from the head and neck, accom- 

 panying the jugular veins into which they partly enter. 



VAS DEFERENS, see Eeproductive Organs (p. 784 and fig. 

 p. 782). 



VEERY, a name in North America (Nuttall, Man. Orn. i. 

 p. 349) for what is otherwise known as Wilson's Thrush, Turdus 

 fuscescens. 



VEIN (adj. venous). Veins are the vessels through which 

 the blood flows into the heart, no matter if this blood be venous, 

 or arterial like that which returns purified from the lungs through 

 the pulmonary veins. The walls of the veins are thinner than 

 those of the arteries, and, especially toward the extremities, 

 contain numerous valves to hinder the reflux of the blood. 

 Similar veins guard the entrance to the heart, but there are none in 

 the jugular, trunk and cutaneous veins (see p. 1008). 



VERTEBR.^, see Skeleton (p. 848). 



VIREO, the name of a genus proposed by Vieillot in 1807, and 

 long since used as English, for some North-American birds, sometimes 

 called Greenlets. With some allied genera they seem to form 

 a small liut recognizal)le Family, very character- 

 istic of the " Columbian " Fauna. They are 

 mostly inconspicuous in their olive-green plumage, 

 Init like the Alaudidx (Lark) are instructive to 

 the taxonomer, teaching him not to depend on Vieeosylvia. 



the number of primary quills, and also shewing ^^ wamson.) 



a considerable amount of diff'erentiation of form within certain 

 limits, though some of the species are not easily distinguished. 

 By most systematists they are supposed to be allied to the Laniidm 

 (Shrike), and by some are even included in that Family, but 

 on grounds that are at least debatable. Baird in 1866 {Bev. Am. 

 B. pp. 321-400) insisted forcibly on the distinctness of the Vireo- 

 nidai, to Avhich he assigned '7 geuei-a and some subgenei-a, being 

 therein followed in 1873 by Messrs. Sclater and Salvin {Nomend. 

 Av. pp. 11-13); but Sundevall in 1872 {Teniamen, p. 13) had 



