DISCUSSION 
85 
In addition to the above six, a number of other cases have been 
published with detail insufficient for the purposes of our present comparison, 
but it may be noted that in some instances the absence of a corpus luteum 
has been recorded, while one or two observers state that they were unable 
to find any lutein tissue round the gestation sac. 
It is apparent from the analysis of these six cases, and the description 
of the present specimen, that considerable variety occurs in the imbedding 
of the blastocyst in the ovary, more especially in respect to its relations 
to the corpus luteum. Upon one point all observers are agreed, viz., that 
the layer next to the foetal tissue is connective tissue in some form, 
and that the lutein cells do not play the part of decidua; indeed, 
histologically they appear to take no share in the imbedding of the ovum. 
The published cases may be divided into three categories according to the 
relationships of the lutein tissue. (1) It may occur all round the gestation 
sac, as in two of the cases cited and several others referred to by Kelly and 
MTlroy ; (2) it may appear only on one aspect of the gestation sac, as in 
four of the instances given above; and (3) it may be absent altogether 
either as a separate layer or as an intact corpus luteum, as in several 
cases not here summarised, e.g. the cases of Freund and Thome. The 
second group of cases may be further subdivided into a group in which 
the corpus luteum is quite intact, e.g. Hewetson and Jordan-Lloyd’s 
case, and a group in which there is a defect in the wall adjoining the 
gestation sac, e.g. in the present case and that of Franz. 
Before proceeding to explain the differences which the analysis of the 
cases reveals, the structure and development of the normal corpus luteum 
may be briefly considered. 
The origin of the lutein cells is still a matter of controversy, 1 but 
as regards the human subject the preparations of one of us (J. H. T.) 
seem quite clearly to indicate that, whatever the source of the cells may 
be in lower mammals, they do not in man arise from the membrana 
granulosa. In a Graafian follicle which is approaching maturity, the 
membrana granulosa forms a fairly thick layer of cells even apart from 
the discus proligerus. Outside this there is seen a layer of large oval 
1 See a lie view by F. H. A. Marshall in Q.J. of Micro. Sc. 1905. 
