DEVELOPMENT OF THE CHICK. 201 



At each end* of the yolk, towards the long axis of the egg, we may 

 observe a white substance going out, about the size of a white thread, 

 which does not come out at once, but as if its attachment Avas spread on 

 the yolk, or that it was the membrane of the yolk contracting and 

 sending out the cord. It passes towards the end of the egg, and appears 

 to be increasing in size, more loose in texture, as if gradually dissolving 

 and swelling, and towards its termination it looks like a cloud, or white 

 fumes in the air. These two threads are the axes on which the yolk 

 turns, and keep its lightest side always uppermost. As the most di- 

 stinct part or terminations of these threads do not turn with the yolk, 

 the thread, or that end which is nearest to the yolk, must twist when 

 the egg is turned ; and if the egg is turned oftener in one way than what 

 the threads can twist, then the yolk must turn round with the egg ; but 

 as it is not likely this can ever happen in any natural process, no such 

 inconvenience can ever occur. 



On one side of the yolk is a lighter spot than any of the other, 

 which is called the ' cieatricula ;' in this is the chick formed ; but before 

 incubation no traces of the embryo can be discovered, there being no 

 difference between this part that is impregnated, and one not impreg- 

 nated 1 . 



The ' slime ' is a secretion from the oviduct t, and is collected by the 

 yolk in its passage along this duct, in its way to the shell-forming part, 

 by which means it surrounds this yolk everywhere, but mostly at the 

 two ends, as the egg is of an elliptical form : and here it appears to 

 adhere to the inner membrane more than anywhere else, probably in 

 some measure connected with the two ends above described. It is 

 transparent, having a slight tinge of a yellow in it. Its attraction of 

 cohesion is such, as allows it to have its figure very much altered, and 

 recovering itself somewhat like an elastic body ; therefore not a fluid 

 whose parts can be moved on each other, and always keep the place 

 they are moved into. It coagulates into a white substance, which 

 appears to be lamellated. 



* I call these ' ends ' because they are towards the long axis of the egg. 



t Birds have but one oviduct when grown up, although two are originally formed ; 

 but it is the left only that remains. In my maiden Preparation 2 there was one on 

 the right side, but it was a kind of dwarf one. This duct is thrown into consider- 

 able convolutions (therefore much longer than what was only necessary for a duct), 

 having a meso-oviduct. It may be said to consist of five parts, which are in some 

 degree different in structure. The first may be called the mouth or fimbria, which 

 is an oblique opening looking [like] a slit. 



1 [This similarity can only be understood as referring to the absence of visible 

 traces of the embryo.] 



2 [Probably No. 2731.] 



