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 descrihed iu the present note {loc. cit. 

 p. 236) :— 



" Independamment de ces deux faisceaux musculaires que Ton 

 retrouve avee la meme disposition chez tous les oiseaux, j'ai observe 

 chez les Eudijptes au niveau de I'ongle forme en dehors par le 

 diaphragme thoraco-abdoniinale etla portion infcrieure dn diaphragine 

 thoracique, ua faisceau rnusculaire a fibres pales et divergentes. 

 Ces fibres sont dirigees suivaut le contour qu'affecte en leur point 

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

 terminent toutes par un sommet aponeurotique. Je de'signerai ce 

 muscle par I'appellation de muscle diaphragmatique transverse." 



It appears therefore that the Puffins as well as the Penguins and 

 Ducks are to be distinguished from many other birds by the fact that 

 the oblique septum is partially covered by a layer 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 

 {Bhamphastos ariel) a perfectly similar patch of muscle occupying 

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

 obviously uustriated. 



'i'here is another important difference between the muscular layer 

 of the oblique septum in the Duck and that in the Puffin. 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 iu 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 umjecessary to insist upon the homology of the muscular layer 

 in the two cases. 



Mr. C. 1\ 3Iarshall, 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 the part of tiie muscle. The 

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

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

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

 Hamann. The pedicellarice are undoubtedly the most actively 

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

 (striate) supports the views of Mr. Marshall. 



^ Loc. cit. p. 505, fig. 2, m. ^ Q.uart. Jouru. Micr. Sci., Aug. 1887. 



