ON THE THTMUS IN THE MA.BS[JPIA.LS. 537 



The Thymus in the Marsupials. By James John"stone, 



Fisheries Assistant, University College, Liverpool *. 



[Read 21st April, 1898.] 

 (Plates 37-39.) 



The investigation which forms the subject of this paper was 

 pursued at the Eoyal College of Science, London, at the sugges- 

 tion of my former teacher. Prof. Gr. B. Howes, F.R.S., to whom 

 I am deeply indebted for much valuable assistance and for 

 placing at my disposal the adult material upon which I report. 

 I am also grateful to Mr. M. F. Woodward, who helped me 

 greatly, and gave me the pouch-specimens referred to below. 

 In addition I have to thank Prof. Symington, of Queen's College, 

 Belfast, for allowing me to read the manuscript of his paper (1) 

 on this subject, lately published in the ' Journal of Anatomy 

 and Physiology,' which was in the printer's hands while my work 

 was in progress. 



I have examined the following forms : — Didelphys pusilla, 

 Thylacinus, Dasyurus viverrinus^ Antechinomys lanigera^ Pera- 

 meles Gunni, Tricliosurus vuJpecula, Cuscus orientalis, Petaurus, 

 and Phascolarctus cinereus, all adult specimens. I have also cut 

 serial sections of pouch-specimens oi Didelphys murina, Dasyurus 

 viverrina, Myrmecohiusfasciatus, Perameles, Trichosurus vtdpecula, 

 Macropus Wilcoxii, and Macropus Eugenii. It is unnecessary to 

 recapitulate the history of our knowledge of this subject, since 

 that has been so recently done by Prof. Symington in the paper 

 mentioned, except to add that,, in addition to the papers referred 

 to by him, there is one by Otto (3) in which the thymus is 

 described in Didelphys, Macropus, Petrogale, and Hypsiprymnus. 

 I propose to describe the topographical anatomy of the thymus 

 in genera and species hitherto unexamined, and to record the 

 fresh facts which I have observed. 



I. Didelphyid^. 

 Didelphys pusilla. Adult specimen. (PI. 39. fig. 10.) 

 The thoracic contents were hardened and sectioned serially. 

 The thymus (tm.) was very large and occupied the characteristic 

 position in the upper part of the thorax. A delicate prolongation 



* From the Zoological Laboratory, R. Ooll. Sci. London. Cominuaicated by 

 Prof. a. B. Howes, F.R.S., Sec.L.S. 



