MUSEUM OF COMPAKATIVE ZOOLOGY. 29 



uot come in contact with water ; but when immersed in water they 

 soon exchange the flaccid for a more rigid condition, like the eggs of 

 many other fishes. Whether the egg is in water or in air, its surface is 

 excessively sticky, as Mr. S. Garman 1 has already accurately observed. 

 The eggs adhere equally well to polished and to roughened surfaces. 

 When let fall directly from the female into 95 per cent alcohol, with a 

 view to ascertaining if there was any special superimposed layer of viscid 

 substance such as that described by Kupffer ('78 a , p. 178) for the 

 herring, the eggs have furnished no evidence of the existence of any 

 such continuous film, nor of any covering additional to that which is 

 distinguishable in the mature ovarian ovum, except small amber-colored 

 bodies mentioned later. 



When laid the egg of Lepidosteus is enclosed in a single membranous 

 envelope about 50-60 fx thick (Plate I. Figs. 5, 11). This membrane is, 

 however, composed of two distinct but firmly united layers. The outer 

 layer, which embraces from one fourth to one third of the total thickness 

 of the membrane, 2 I shall call the villous layer (st. vil.) ; the inner, the 

 zona radiata {z.r.). The former is the outer covering of "elongated, 

 highly refractive bodies," described by Balfour and Parker ; the latter 

 undoubtedly embraces both the zones — z.r. and z.r J — described by 

 those authors. It will be convenient to consider the two layers together 

 rather than separately. 



Examined in the fresh condition, the outer surface of the egg envelope 

 is of a faintly yellowish or brownish tint, which is in part due to the 

 presence of small ovoid bodies of variable size, of an amber color and a 

 waxy appearance (Plate VIII. Fig. 5), which are scattered over the surface. 

 I am unable to say how or where these bodies are formed, but possibly 

 they result from the disintegration of the granulosa. Aside from these 

 bodies the surface presents a roughened or shagreen-like appearance, 

 which is found upon microscopic study to be due to slightly rounded 

 prominences of nearly uniform diameter which are separated from each 

 other by regular nearly straight lines, so that a view perpendicularly 

 upon the surface (Plate I. Fig. 1) presents a field divided by these lines 

 into small polygonal (four- to six-sided) nearly equal areas. The aver- 

 age size of the areas increases slightly as one approaches the vegetative 

 pole of the egg. When the envelope has been removed and torn 



1 See A. Agassiz, '78 a , p. 66. 



2 Measurements of the fresh membrane of an ovarian egg left twelve hours in 

 glycerine gave a total thickness of 68^, of which 50 [x represented the zona and 18 n 

 the villous layer. After the addition of weak hydrochloric acid the latter increased 

 to twice its original thickness (36 /*). 



