No. 389.] OVUM IN OVO. 413 
II. Enveloping egg of colossal size; complete; blastoderm probably 
present. 
Enveloped egg: 
(a) Without shell, but otherwise complete. In this case a common 
shell may surround two or three eggs complete except for shells 
and shell membranes ; forming “ double-yolk ” or “ triple-yolk ” 
eggs. 
(2) One of the enclosed eggs of normal appearance and size, 
possessing shell, albumen, and yolk; the other eggs surrounded 
by a common shell, but having no shells of their own. 
According to the accepted accounts, the yolk of the fowl’s 
ovum is of normal size when it leaves its vascular capsule in 
the ovary, and is taken up by the infundibulum. Reaching the 
oviduct it receives its first layer of albumen, and is carried 
slowly down the tube by peristaltic muscular contraction of the 
walls. Near the lower end of the oviduct the final layers of 
albumen are added, and in the distal extremity of the duct, 
called the uterus, the shell is formed. 
In the opinion of several writers the small included egg 
represents a fragment of a normal ovum which has been 
' ruptured, and thus has parted with some of its substance 
after leaving the ovary. This fragment is then treated in the 
oviduct like a full-sized egg. The small egg-like body thus 
produced is sometimes laid, but occasionally it is driven by anti- 
peristaltic action up the tube until it collides and fuses with the 
mother egg. This theory will suffice to explain the first class 
of inclusions on the supposition that rupture takes place in the 
upper part of the oviduct, or at least after the first layers of 
albumen have been added to the normal egg. Since the small 
included eggs are generally yolkless, we must infer that such 
ruptures are, as a rule, confined to the albumen. It seems more 
probable that the small egg becomes enclosed before the shell 
membrane is formed over a normal egg, with little if any 
retrogressive movement. Furthermore, it is possible that 
any substance which serves as a local stimulus to the upper 
part of the oviduct, whether coming from the ovary as abortive 
egg or egg-fragment, or from the duct as secreted product, may 
serve as a nucleus, about which an egg-like body may be formed. 
Normally laid eggs, indeed, tend to sweep the oviducal canal 
