66 BULLETIN OF THE 



The orifices of the micropyle are so small on hardened eggs that it is 

 probable that they are narrowed by the action of the reagents, which 

 also cause a retraction of the capsule of the egg. For this reason it is 

 very difficult to find these orifices." 



The micropylar apparatus is composed of several (5 to 13) orifices, 

 and Salensky states that, although he has examined a great number of 

 eggs, he has never found two which were identical either in the number- 

 or distribution of the orifices. " Each orifice consists of a quite small 

 pit (fossette) having the form of a crater ; it is surrounded by small, 

 very slender cylinders." 



Salensky has given only surface views of the micropylar region, but it 

 has occurred to me that his " very slender cylinders " may be villi which 

 surround the crater-like depression. They would appear to have a radial 

 arrangement about the crater as a centre, if the villous layer were seen in 

 optical section at a plane a little below the outer margin of the crater. 



d. Dipnoi. 



The conclusions reached by Beddard ('86*) relative to the ova of 

 Lepidosiren possibly rest on too limited material to receive immediate 

 acceptance. So far as regards the egg membranes, the story is certainly 

 far from being satisfactorily completed. In the youngest eggs there was 

 no trace of any membrane ; but as development proceeded, a delicate 

 homogeneous membrane encircled the ovum. This was from analogy 

 thought to be the product of the egg protoplasm, even though it was 

 more firmly adherent to the follicular epithelium than to the ovum, 

 and it is called vitelline membrane. In more mature ova there was 

 underneath this a much thicker radially striate membrane, probably 

 corresponding to the zona radiata of other vertebrates, which in places 

 seemed to pass gradually into the substance of the protoplasm. This 

 membrane (zona radiata) began to disappear with the first steps in the 

 formation of yolk. During the period of yolk formation the vitelline 

 membrane became thicker, and also radially and coarsely striate. The 

 author believes that there was a stage which succeeded this, during 

 which there was no membrane of any kind, and that at this time an 

 immense number of follicular cells migrated into the yolk. But in 

 addition there followed still another stage, — when the ovum was en- 

 tirely occupied by yolk, — in which the epithelium was separated from 

 the contents of the ovum by an extremely delicate homogeneous mem- 

 brane, which either corresponded (in some cases) to the persistent vitel- 

 line membrane, or (in other cases) was a new formation ; but even in 



