THYMUS IN THE MAKSUPIALS. 555 



tract uniting these two bodies may be compared witb one of the 

 epithelial corpuscles, probably the internal one, and the cervical 

 thymus itself with the internal thymic lobule which is usually 

 found in the thyroid of the mammalia. The other (external) 

 corpuscle would thus be absent. I have not cut serial sections 

 of the thyroid of any marsupial possessing a cervical thymus, 

 but in such the internal thymic lobule of the thyroid may not 

 unreasonably be expected to be absent ; and it is suggestive in 

 this connexion that in the young Perameles, where a cervical 

 thymus is absent, indications of such an ^intra-thyroid thymic 

 nodule are present. 



But in the lack of any exact knowledge of the development of 

 these organs, such explanations can only be tentative. 



References. 



(1) Symington, J. — " The Thymus in the Marsupialia." Journal 



of Anatomy and Physiology, Jan, 1898, pp. 278-291. 



(2) Symington, J. — " JJehev Thyroidea, Qlanclulce parathyroide(S 



und Tliymus beim dreizehigen Faulthier (Ai', Bradypus 

 tridactylus)." Archiv filr Anat. und Physiologic, Supple- 

 ment-band, 1897. 



(3) Otto, M. — " Beitrage z. vergleichd. Anatomic der Glandula 



thyroidea und Thymus der Saugethiere." Ber. Naturf. 

 G-esellsch. Preiburg-i-B., Bd. x. pp. 33-90, 1897. 



(4) Welsh, D. A. — " Concerning the Parathyroid Glands." 



Journal Anat. and Physiology, 1898, pp. 292-307. 



(5) Metteon, p. de. — " Eecherches sur le developpement du 



Thymus et de la Glande thyroi'de." EecueilZool. Suisse, 

 1886, torn. iii. pp. 517-629. 



(6) Peenant, a. — " Contribution a I'etude du developpement 



organique et histologique du Thymus." La Cellule, 

 tom. X., 1894, pp. 85-184. 



(7) Kohn, a. — " Studien iiber die Schilddrlise." Archiv fiir 



mikr. Anat., Bd. xliv. pp. 366-422. 



(8) Simon, C. — " Thyroi'de laterale et Griandule thyroi'dienne chez 



Ics Mammiferes." Nancy, 1896. 



