TR.VN'SACTIO.NS OF SECriON' D. DEn. ANATOMY AND rilYSIOLOGY. 557 



both in Elasmobranchs and Mammals, publishing a paper upon it in 1878.^ A paper 

 published in the same year,"on the ' Maturation and Impregnation of Ihe Ovum,' 

 contained the very ingenious suggestion that the easting out of the polar bodies 

 prevents the ovum developing by itself into a new individual, i.e. prevents parthe- 

 nogenesis ; and Balfour points out that parthenogenesis is practically confined to 

 the arthropoda and rotiiera, which are the only two groups in which polar bodies 

 are not known to occur. 



Balfour still continued, now in conjunction with Sedgwick, his researches on the 

 urino-genital system, and described, among many other new points, the existence 

 of a head-kidney (pronephros) in the chick. - 



In this year, Balfour also investigated ^ the earlj' development of Lacerta, and 

 pointed out the presence of a primitive streak and of a neurenteric canal. This 

 investigation confirmed his belief in the hypothesis previously quoted that the 

 primitive streak is the relic of a blastopore. 



At this time Balfour was working hard at his text-book of ' Comparative Em- 

 bryology.' His published papers were no less numerous than before, but consisted 

 in part of extracts from the more speculative chapters of the forthcoming book. 

 He, however, published a paper,'* containing the results of work scattered over two 

 years, on the development of Spiders. He also published a paper * on the skeleton 

 of the paired fins, based upon his work on Elasmobranchs. In this he contests the 

 views of Gegenbauer and Huxley, that the primitive fin consists of a central multi- 

 segmented axis with many lateral v&ja, and is most nearly retained in Ceratodus; 

 he rather considers the primitive form to be a longitudinal bar running along the 

 base of the fin (basipterygium), and giving oft' at right angles series of rays which 

 pass into the fin. He adheres to the view expressed in the ' Elasmobranch Fishes ' 

 (p. 101) that the vertebrate limbs are remnants of two continuous lateral fins. 



Another important paper of the same year dealt with the placenta. Balfour 

 supposed that in the primitive Placentalia, simple foetal villi, like those of the pig, 

 projected from the discoidal allantoic region of the chorion into uterine crypts. The 

 deciduate discoidal placenta of Rodents and Tnsectivores is the first stao-e in 

 advance of this primitive type. Then along different lines diverge the zonary 

 placenta of Carnivora, and tbe diffuse placenta of Suidfe, Lemuridfe, &c. ; and the 

 latter becomes contracted down to the discoidal placenta of man, a form in no way 

 to be confounded with the primitive discoidal placenta of Rodents. 



He engaged also, in conjunction with Mr. Wm. N. Parker, in a verv important 

 research, to be published in full in the ' Philosophical Transactions,' on'the 'Struc- 

 ture and Development of Lepidosteus.' This paper contains an immense amount of 

 new matter, both anatomical and embryological, and shows that Lepidosteus, though 

 a true ganoid, has very marked teleostean affinities. 



Balfour's last published paper,« which appeared during his recent illness, was 

 written with the assistance of Mr. Beighton, and related to the germinal layers of 

 the chick. This paper describes, in a very beautiful way, the double orio-inof the 

 mesoblast, partly from an axial strip of epiblast in the line of the primitive streak 

 and partly as two lateral plates differentiated from the hypoblast in front of the 

 primitive streak. 



Before his last, fatal journey, Mr. Balfour was engaged in preparing a new 

 edition of the ' Elements of Embryology,' and in producing a vei-y elaborate memoir 

 on the ' Anatomy and Development of Peripatus.' He had previously investio^ated 

 that animal, in 1879, and had cleared up the matter of its segmental organs (over- 

 looked by Moseley), and demonstrated the presence of ganglia on its ventral nerve- 

 cords. 



Mr. Balfour became a member of this Association in 1871, the year after he 



' Quarterly Journal of Microscopical Science, vol. xviii. 1878. 



^ Proceedings of the Boyal Society, vol. xxvii. 1878. 



' Quarterly Journal of Microscopical Science, vol. xix. 1879. 



* Quarterly Jpiirmil of Microscopical Science, vol. xx. 1880. 



* Proceedings of the Zoological Society, 1881. 



* Quarterly Jotirnal of Microscopical Science, vol. xxii. 1882. 



