160 p. KIDD. 



On Some Points in the Early Development of the Hen's 

 Egg. By P. Kidd, B.A. (With Plate XII.) 



The object of this paper is twofold : 



(a) To describe a peculiarly irregular form of segmenta- 

 tion observed in several eggs. 



[h) To discuss the relations of the germ and the large 

 formative cells lying on the floor of the subgerminal cavity, 

 to the finely granular material forming the floor of that 

 cavity in the first hours of incubation. 



(a) The only observations on irregular segmentation that 

 I can find are those relating to — 



(i) The appearances of unfertilised eggs when freshly laid, 

 or when taken from the oviduct. 



(ii) The changes occurring in such eggs after incubation. 



A full account of such observations is given by Oellacher, 

 * Zeitsch. fiir Wissensch. Zoologie,' Bd. 22 (" Die Veran- 

 derungen des unbefruchteten Keimes des Hiihnereies im 

 Eileiter und bei Bebriitungsversuchen "). 



Oellacher quotes the earlier researches of Dumas and 

 Prevost., ' Zeitsch. fiir Organ. Physik./ 1828, and states 

 that his results agree more or less with theirs. Oellacher 

 finds that unfertilised hens' eggs freshly laid or taken 

 from the oviduct present appearances comparable to 

 those occurring early in the development of fertilised eggs. 

 The blastoderm, in these cases, undergoes segmentation 

 to a greater or less extent, but the further stages in the 

 development of the fertilised ovum are wanting. On incu- 

 bating such eggs for eight hours, the cells of the upper layer 

 of the germ were seen to be smaller than usual at this stage 

 of incubation, especially at the centre ; whereas the peri- 

 pheral cells were much larger and less numerous. 



After incubation for two or three days the central portion 

 of the germ undergoes a retrograde metamorphosis, and is 

 gradually replaced by a finely granular mass. The cells at 

 the periphery at the same time become smaller and more 

 numerous, and they all finally undergo a similar granular 

 change. 



On the fifth day of incubation solution of the germ and 

 yolk took place. Oellacher's investigations were not carried 

 further, as there seemed to be no object in doing so. 



Bischoff" ('Ann. des Sciences Nat.,' iii ser., Zool., t. ii) 

 found segmentation in the unfertilised ova of the frog and 

 the sow, and Leukart (art. Zeugung, * Wagner's Handwb. 



