REPORT ON THE SPHENISCID^. 209 



In Spheniscus demersus, Spheniscus magellanicus, and Spheniscus minor, the 

 insertion of the contractores extends farther back than in JEudi/2Jtes, and reaches a point 

 exactly opposite the tracheal bifurcation. In the two former, as in Eudyptes chrysocome 

 from Kerguelen, the two muscles of opposite sides are in contact along the upper surface 

 of the trachea for the posterior half of that tube. Such is not the case in Spheniscus 

 minor. In Sioheniscus mendiculus the insertion of the contractor falls short of the 

 bifurcation by ^ an inch. 



In Pygosceles tceniatus the contractores are inserted f of an inch in front of the 

 bifurcation, and, as in Spheniscus demersus and Spheniscus magellanicus, the muscles 

 of opposite sides are in contact along the upper surface of the trachea for the posterior 

 three-fourths of the tube. 



Lastly, in Aptenodytes (PI. XVIII. figs. 8 and 9), the insertions of the contractores 

 reach a point exactly opposite the bifurcation of the trachea. In this species the muscles 

 are relatively more powerful than in any other, the two muscles being in contact both 

 above and below the trachea, so that they form a muscular sheath which entirely envelopes 

 the posterior two-thirds of that tube. 



If now wo compare the difierent genera in respect of the insertion of this muscle, it 

 appears that Aptenodytes agrees with Spheniscus (with the exception of Spheniscus 

 mendicidus), in as much as the contractores extend as far back as the tracheal bifurcation. 

 Pygosceles, on the other hand, agrees with Eudyptes, in as much as the insertion of the 

 contractores is situated from ^ to f of an inch in front of the bifurcation. Spheniscus 

 mendiculus agrees with Eudyptes rather than with the other species of its own genus, 

 but it is possible that the point of insertion of these muscles in the single specimen 

 examined may not prove constant in other specimens of the same species. 



Variations in respect of the Trachea and Bronchi. 



The variations in respect of the trachea and bronchi in various species of Penguin 

 from the arrangement above described in Eudyptes chrysocome from Tristan are referrible 

 to three points. Firstly, the relation of the posterior extremities of the contractores tracheae 

 to the lower larynx ; secondly, the number of rings, tracheal and bronchial, which 

 participate in the formation of the syrinx ; and thirdly, the extent of the septum tracheae. 



With regard to the first of these points, it will have been observed that, as shown 

 above, in certain species, e.g., the various species of Eudyptes, in Pygosceles, and in 

 Spheniscus mendiculus, the contractores tracheae fall short of the tracheal bifurcation, 

 while in others, such as Aptenodytes and the remaining species of Spheniscus, the con- 

 tractores extend as far back as that point. In the former group, therefore, the lower 

 larynx is altogether destitute of muscles, while in the latter it is provided with a single 

 pair, to wit, the posterior extremities of the contractores. That a generic distinction 

 cannot, however, be founded on this fact is shown by the occurrence in Spheniscus mendi- 



(aOOL. CHALL. EXP.— PAUT XVIII. — 1883.) S 27 



