TRANSACTIONS OF SECTION D. 771 



19. Note on a Point in the Structure of Fratercula Arctica. By Frank E. 

 Beddard, M.A., Prosector to the Zoological Socieiy of London. 



The posterior region of the oblique septa in this bird is largely muscular, as is 

 stated by Huxley (' Proc. Zool. Soc' 1882, p. 566) to be the case in the duck. 

 This fact is au additional point of similarity between the representatives of these 

 two orders of birds, which are placed by some naturalists near together. Tlie 

 presence of this muscular tissue in the oblique septum has, however, an obvious 

 use, which, perhaps, rather does away with its value as evidence of affinity. The 

 birds in question have an elongated sternum, and accordingly the abdominal 

 muscles are necessarily less in extent than in many other birds. The process of 

 respiration in birds depends to a large extent upon the abdominal muscles which 

 •depress the sternum, and therefore exert pressure upon the underlying air-sacs. 

 In diving birds it is clear that there is, if anything, need of greater force for the 

 expulsion of air than in flying or wading birds ; the presence therefore of muscular 

 fibres on the oblique septum enables this structure to be utilised as au additional 

 depressor of the sternum. 



Professor Huxley in the paper referred to compares the oblique septum of the 

 bird to a structure in the crocodile, which consists of a broad thin muscle on 

 either side arising from the pubis, and attached to ventral face of pericardium and 

 to the ventral and lateral parts of the fibrous capsule of the stomach. He does 

 not, however, lay special stress upon the particular resemblance which this 

 structure bears to the oblique septum of the duck (and of the pufiin) on account 

 of the presence of muscular tissue in these birds. This is another instance of 

 an ancient character being retained in a bird which is not one of the Struthionidte, 

 and is still further evidence against regarding these birds as the most archaic living 

 form of bird. 



'2.0. On the Development of the Ovum mEudrilus.^ By Frank E. Beddard, 

 M.A., Prosector to the Zoological Society of London. 



The process of growth of the ovarian ovum in this aberrant earthworm differs 

 in detail from the corresponding processes in any other annelid. In each ' com- 

 partment ' of the ovary (see ' Proc. Eoy. Soc, Edin.' 1885-6, p. 672), only a few 

 germinal cells become ova ; the remaining cells become for the most part meta- 

 morphosed into a semi-fluid mass of protoplasm. The nuclei of these cells are 

 at fii'st recognisable, but afterwards degenerate. A certain number of cells form a 

 cap situated at one pole of the ovum, which when mature is surrounded by a single 

 vitelline membrane. These changes in the germinal cells which do not become 

 ova appear to indicate that they take a share in the nutrition of the ovum. 



Sub-Section BOTANY. 



1. Alternation of Generations in Green Plants. By J. Reynolds Yaizet. 



The object of this paper is twofold. First, to discuss the origin of alternation 

 of generations in all green plants. Second, to see what efiect such a view has on 

 comparisons between the vegetative bodies of the oophyte and sporophyte of the 

 same or diflerent species. 



Comparisons of the life-histories of Coleochate, (Edogonium, Spliceroplea, Hydro- 

 dictyon, Fandorlna, also Chara and the Floridece, with that of the lowest mosses, 

 show that in all these forms there is virtually an alternation of generations. In the 

 lowest forms the sporophore generation is shown to consist of a simple mass of 

 cells produced by the division of the oospore, each cell becoming sooner or later a 

 spore which gives rise to the vegetative body of the oophyte ; in the simplest case, 

 namely, Fandorina, the oospore sometimes gives rise directly to a sino-le sexual 



' Journ. Anat. Phys. October 1887. 



3 D 2 



