346 
Proceedings of Royal Society of Edinburgh. [july 4, 
Simple inspection of the graduated probabilities shows that they 
proceed with sufficient regularity. They will also satisfy the other 
criterion of a good graduation, if the number of childless marriages, 
as calculated from them, does not differ much from the actual 
number. A comparison of this kind is made in the following 
table : — 
Table K. — Comparison of the actual and the calculated Numbers 
of Childless Marriages in Quinquennial Groups of Ages. 
Men who married as Peer or 
Heir-Apparent.. 
Men who did not so marry. 
Ages at 
Marriage. 
N umber 
Childless Marriages. 
Number 
Childless Marriages. 
of 
Ol 
Marriages. 
Actual. 
Calculated. 
Marriages. 
Actual. 
Calculated. 
16-24 
140 
18 
17 "5 
199 
26 
30-6 
25-29 
134 
17 
17 T 
333 
67 
61-7 
30-34 
82 
8 
11*4 
218 
45 
48-8 
35-39 
45 
10 
7’9 
112 
31 
29-9 
40-44 
28 
9 
6-6 
62 
20 
19-6 
45-49 
20 
6 
6*5 
41 
15 
15-0 
50-54 
16 
4 
6°5 
19 
8 
9-3 
55-59 
18 
10 
9*4 
12 
10 
8-5 
60-64 
15 
10 
10-5 
8 
7 
7-0 
65-69 
9 
8 
7-3 
3 
3 
2‘8 
70-74 
5 
5 
4-5 
75-79 
3 
3 
3-0 
... 
... 
515 
108 
108-2 
1007 
232 
233-2 
In conclusion it may be useful to remind my readers that I have 
considered a marriage to be fruitful, if any child has been born, even 
although all the children born of the marriage may have died 
young. 
3. On the ISTephridia of Hirudo medicinalis. By Dr A. B. 
Griffiths, F.R.S.E., F.C.S. (London and Paris) ; Prin- 
cipal, and Lecturer on Chemistry and Biology, School 
of Science, Lincoln. 
The nephridia of Hirudo medicinalis , as is well known to bio- 
logists, are in pairs extending from the second to the eighteenth 
segments (somites). Each nephridium consists of a much convo- 
luted cellular tube. The cells of the tube are perforated by small 
