412 THE AMERICAN NATURALIST.  [VOL. XXXIII. 
remark that the foregoing are the only cases recorded of this 
singular abnormal production, but that it would be possible to 
cite more than thirty instances in which small yolkless eggs 
have been found enclosed in another egg apparently normal. 
Later additions to this literature have been made by Landois in 
1882,! and by Schumacher in 1896.” 
Landois remarks that in most cases of ovum in ovo the 
included egg is small and yolkless, and sometimes possesses a 
very abnormal form. In one erratic individual it resembled 
a tapeworm, consisting of a button the size of a pin head, 
followed by a fibrous section, and ending in a broad flattened 
string. He thinks that most so-called tapeworms in hens’ eggs 
are nothing more than monstrosities of this kind. 
In the case described by Schumacher the enclosing egg was 
apparently normal, and, like that figured by Patrona and Grassi, 
possessed an egg-like inclusion in the albumen. This was of 
regular oval form, a little larger than that here described, and, 
besides hard shell, possessed a stratified albumen, an irregular 
spirally twisted yolk mass, measuring 8 x 4 mm., with small 
chalazze at either end. There was no blastoderm. 
III. 
Reviewing the cases of ovum in ovo in zoölogical literature, 
we may classify them in the following manner : 
I. Enveloping egg usually normal, but occasionally of large size; blasto- 
derm recorded in at least one instance. 
Enveloped egg: 
(a) In yolk; small; composed of shell, shell membrane, albumen, 
and yolk; no blastoderm known to occur in this or in the 
following variations ; single case recorded in this paper (Fig. 2). 
(4) Inalbumen ; small; composed usually of shell, shell membrane, 
albumen, and rarely with yolk; few cases reported 
(c) In albumen; small; usually with shell, shell membrane, and 
albumen, but no yolk; most cases of ovum in ovo reported are 
of this kind (Fig. 3). 
(d) In albumen; usually small and variously distorted, so as to 
bear little resemblance to an egg at all. 
1 Fremde Einschliisse in Hiihnereiern. Humboldt, Heft 1 (1882), pp. 22-24. 
? Ein Ei im Ei, Zoologischer Anzeiger, Bd. xix (1896), pp. 366-368. 
