254 MR. F. E. BEDDARD ON THE [May 1, 



quotation from his paper will show that he prohably refers to a 

 structure identical with that described in the present note (loc. cit. 

 p. 236) :— 



" Independamment de ces deux fiiisceaux musculaires que Ton 

 retrouve avec la nieme disposition chez tous les oiseaux, j'ai observe 

 chez les Eudi/ptes au niveau de I'ongle forme en dehors par le 

 diaphragme thoraco-abdominale et la portion infe'rieure dn diaphragme 

 thoracique, un faisceau musctilaire a fibres pales et divergentes. 

 Ces fibres sout dirigees suivant le contour qu'affecte en leur point 

 d'existence la cavite abdominale. Elles sont assez courtes et se 

 teriniiient toutes par un sommet aponeurotique. Je designerai ce 

 muscle par Tappeliation de muscle diaphragmatique transverse." 



It appears therefore that the Puffins as well us the Penr/uins and 

 Ducks are to be distinc/uished from many other birds by the fact that 

 the oblique septum is partially covered by a Uu/er of muscular fibres. 

 But this layer of muscular fibres is by no means equally developed 

 in all the three groups of birds. It is best developed in the Puffin and 

 in the Penguins ; it appears to be very feebly developed in the Duck. 

 Prof. Huxley gives no particular description of it in the Duck, but 

 his figure ' shows that the layer of muscular fibres is very limited in 

 extent and does not reach nearly as far as the sternum. It is 

 attached to the dorsal middle line of the body and. only covers the 

 oblique septum for a very short way. I have found in the Toucan 

 {Rhamphastos ariel) a perfectly similar patch of muscle occupying 

 an identical position ; the muscular fibres in this case also were 

 obviously unstriated. 



There' is another important difference between the muscular layer 

 of the oblique septum in the Duck and that in the Pufiin. The 

 fibres are in the Duck {according to Prof. Huxley) and in the 

 Toucan unstriated; in the Puffin they are distinctly striated: I 

 unfortunately neglected to observe whether this was also the case 

 in the Penguins, and Filhol makes no mention of the point. 



It does not, however, as it appears to me, affect the question of 

 the homology of the muscular layer covering the oblique septum in 

 these three types to learn that the fibres are striate in the one and 

 unstriate in the other. 



The muscular fibres of the alimentary tract are commonly said to 

 be striated in the Tench, while they are unstriated in other fish. 

 It is unnecessary to insist upon the homology of the muscular layer 

 in the two cases. 



Mr. C. 1\ Marshall, in a paper upon the histology of muscle ^ 

 points out that striation in the fibres of muscle-bundles appears to be 

 associated with greater activity on tiie part of tlie muscle. The 

 muscles, for example, of an Echinus are for the most part unstriated ; 

 those muscles which move the valves of the ijedicellarise are striated, 

 as was shown by Mr. Geddes and myself, and more recently by 

 Hamann. The pedicellarise are undoubtedly the most actively 

 moving organs of the Echinus ; and the nature of their muscles 

 (striate) supports the views of Mr. Marshall. 



I Loc. cit. p. 5G5, fig. 2, m. ^ Quart. Journ. Micr. Sci., Aug. 1887. 



