544 
DR. MARTIN BARRY’S RESEARCHES IN EMBRYOLOGY. 
gard the round white spot or cicatricula on the yelk of the Bird’s laid egg as an 
altered state of the discus vitellinus in the unfecundated ovarian ovum. So far from 
thinking that such is the case, I venture to believe that the whole substance of the 
cicatricula in the laid egg of the Bird has its origin within the germinal vesicle in 
the same manner as in the ovum of Mammalia^, and therefore that the cicatricula 
in the Bird’s laid egg may properly be called the germ 
No fixed Relation between the Degree of Development of Ova and their Size, Locality, 
or Age. 
365. In my last memoir it was shown that at early periods the several parts of the 
ovum do not necessarily keep pace with one another, and that there is no fixed relation 
between the size of the entire ovum and the degree of development of its most essential 
part. Of the latter fact, many figures in the present paper afford further proof, and 
show that the statement is applicable to ova still within the ovary §. The ovarian 
ovum Plate XXII. fig. 162, measured yt'"> though it had not undergone fecunda- 
tion ||. That in Plate XXIII. fig. 172, was certainly fecundated, but it measured 
only Yt 1 ". The ovum Plate XXV. fig. 1 96, measured W", but was less advanced in the 
essential part than that in fig. 1 98, which had less than half its diameter. Several 
other instances of this kind will be found on comparing the figures. The large size, 
however, which ova in some instances attain without the germ being proportionably 
developed, is referable mainly to the quantity of fluid imbibed by the chorion; for 
before the formation of this membrane the irregularity in question is not so great. 
This will be seen on reference to the Table, par. 428, in which the measurements of 
the chorion and membrane f in many ova have been recorded *jj. 
366. There are two other ways in which irregularity occurs, namely, in regard to 
time and place. The ovum Plate XXV. fig. 196, was taken from a Rabbit killed sixty- 
six hours post coition ; that in fig. 198, though more advanced, was only 5^ hours old, 
that is one-twelfth the age. And if these two ova be compared with regard to their 
local situation, the difference will be found equally remarkable. The older and larger, 
but less developed ovum, fig. 196, was found in the uterus; the younger and smaller 
but more developed ovum, fig. 198, was still within the ovary. These, however, are 
enter entirely into the formation of single accumulations, which through furrows and a pellucid substance be- 
come separated from one another, hut subsequently again become confluent and coalesce.” (Zur Morphologie 
Reisebemerkungen aus Taurien, p. 102.) 
f The principal of the changes producing it having, perhaps, taken place before the ovum left the ovary. 
+ See also “ Second Series,” par. 318. and Notes. 
§ As the ova for the most part are shown as magnified the same number of diameters, the fact here referred 
to may be easily attested by inspection of the Plates. 
|| It was taken indeed from a Rabbit which had not had connexion with the male. 
If the figures in Plate XXVII. be compared, it will be seen, however, that fig. 234, an ovum among the 
most developed in its essential part, has a very small membrane /. 
