FORMATION OF THE GERMINAL LAYERS IN TELEOSTEI. 211 



careful examination of the peripheral row of yolk spheres shows that as yet 

 there is little irregularity in their size and position. So much for the appear- 

 ances presented by an optical section; let us now turn our attention to a 

 stained section of the same stage. Such a section is represented in fig. 7. 

 Remembering the structure of the ripe unfertilised ovum, it is easy to see now 

 that the germinal disc is in process of formation. The protoplasm in collecting 

 towards the surface has followed certain channels between the yolk spheres. 

 There is still, however, a considerable portion of the protoplasm mixed amongst 

 the yolk in the form of branching processes communicating with the surface 

 layer. These processes vary in thickness, and also in their number and distri- 

 bution in different parts of the circumference. Towards the germinal pole they 

 are stronger, and penetrate further into the yolk than at any other point. In 

 the yolk pole the filaments rarely penetrate beyond the second row of yolk 

 spheres. The protoplasm is seen to be highly granular, and also to contain a 

 number of small masses of yolk. It will thus be seen that the true relation of 

 protoplasm to food yolk cannot be made out in optical section. 



The appearance of granules in the protoplasm is the first sign of an active 

 vegetative period in the history of the germinal protoplasm. In the section 

 under consideration the digestive process has only just commenced, so that it 

 may be better studied at a little later stage. Fig. 8 represents a section of an 

 egg five hours after fertilisation, and at a time when the germinal protoplasm 

 has almost entirely collected towards the germinal pole. Large masses of yolk 

 are seen to be entangled in the protoplasmic processes, and throughout the 

 germinal disc itself there are a number of yolk masses varying in size. At this 

 stage great activity is manifested by the protoplasm immediately adjoining the 

 yolk, and, as already stated, the whole mass of the germinal protoplasm has an 

 undulating movement. In the living egg it frequently happens that there is a 

 large temporary collection of the germinal protoplasm at the yolk pole. This 

 has been termed the Gegenhugel by Kupffer. Sometimes this accumulation 

 is so large that it may easily be mistaken for the true germinal area. 



At this stage Kupffer describes an appearance in the living egg, which is 

 intimately connected with the growth of the germinal disc. He says that 

 when the germinal protoplasm forms a distinct layer on the surface of the yolk, 

 the surface vacuoles disappear, and there remains only one or a pair of large 

 lacunw in the centre, which are often continued towards the flat base of the 

 germinal disc by a stalk. These have much in common with the latebra of 

 the hen's egg. According to Kupffer, these lacunae are not to be considered 

 as distinct caverns, but as transition areas (Schmelzung sheer de) in which the 

 globular yolk masses are transformed into a more clear and uniform mass. 

 These, he maintains, are to be found till the end of development. Ryder sug- 

 gests that the lacunas, as described by Kupffer, do not normally exist, but that 



