S08 ANIMAL PARASITES. 



the remarkable action of the segmentation of the yelk. This 

 small space (first embryonal cell) passes through the process 

 which has been represented by Bagge. It is only when 

 the small, clear, central space has divided itself into two 

 parts, that the actual segmentation begins, the vitelline 

 grains accumulating around the two small cells thus pro- 

 duced. But when once the clear centre in the egg is divided 

 into two, then the first furrow is formed at the periphery of the 

 yelk. Now the process goes on in the way described by Bagge, 

 Von Siebold, Kolliker, &c. By this first furrow, two globules, 

 similar both in size and colour, have been formed. In the middle 

 of one of these globules, a small cell is now again produced in the 

 first place, before any further division takes place, the globule 

 itself becomes more densely crowded with granules, and darker 

 and more opaque towards the margin. A new line of segmen- 

 tation is produced in it, sometimes in the longitudinal axis, some- 

 times in a divergent direction, and by this means a new globule 

 of segmentation. But before a further segmentation takes place 

 in the globules formed, one or several of these clear central spaces 

 are always first produced, and then only new lines of segmen- 

 tation shoot up, and new globules are produced, which in their 

 number exactly correspond with the number of the globules of 

 segmentation just formed. To continue the first description, we 

 observe that a new line of division immediately goes off obliquely 

 from the second line towards the peripheiy, and consequently 

 four globules of segmentation are produced. From this point 

 onwards the strict order of the formation of new globules of seg- 

 mentation in a progressively increasing series of numbers ceases ; 

 the globules of segmentation, which are pretty equal in size 

 amongst themselves, become rounded off towards the periphery. 

 At the same time, the globules constantly become smaller, more 

 similar and numerous, by the progress of division, until in this 

 way they have acquired the appearance of a mulberry. Upon 

 this the globules arrange themselves into a beautiful and very 

 regular oval, and almost all round this we perceive a light border 

 between the globules of segmentation and the vitelline membrane. 

 The oval then bends in the middle ; the two poles (cephalic and 

 caudal extremities) endeavour to approach each other, and the 

 creature acquires the rough form of a worm without any internal 

 structure. The two poles then pass by close to one another, and 

 the cylindrical form of the embryo constantly becomes more dis- 



