50 J. B. CLELAND. 
A study of the table will show that specific differences 
exist as regards the number of fetuses present. Thus the 
average in 88 pregnancies of Mus musculus was 4.87 
foetuses; in 745 pregnancies of EH. rattus, 6.66; and in 240 
pregnancies of EH. norvegicus, 8.05. The highest number 
found in the common mouse was 9, whilst that for #. rattus 
was 17, and for E. norvegicus 18. I have a recollection of 
finding, in one or other of these two rats, on one occasion 
no less than 24. We have other records of 15 (once) in £. 
rattus; of 17 (once) and 15 (twice) in E. norvegicus; and 
of 11 (once), 10 (twice), and 9 (twice) in M. musculus, 
whilst my assistant, Mr. R. Grant, has seen 14. 
In Mus musculus the usual number of fcetuses is 4, and 
then 5, followed third in order by 3, 6 and 7. By reference 
to Table II it will be seen that in 44.7 per cent of the preg- 
nancies (38), 4 or 5 foetuses were found; in 84.27, 3 to 7. 
Table II.—Showing the Percentage of Pregnancies to the Total 
Number of Pregnancies for each Number of Fetuses found in utero. 
‘No. of Foetuses| Epimys rattus. | Epimys norvegicus Mus musculus. 
1 35) “4 5°2 
2 8 0 2°6 
3 4°5 1°6 13-1 
4 Day 2 23°7 - 
5 18:2 ) 14:5 a eee 
6 19:4 > 59 7 13-1 
7 21-4 | 17 |\71-6 l134 
8 10:3 12°5 5-2 
9 9°6 20°4 2°6 
10 5°5 | 0 
at 1°8 6°6 0 
12 i 37 0 
13-18 6 Ad 0 
In E. rattus 7, followed by 6, and then 5, were the usual 
numbers. Then comes a big drop to those with 8 fetuses, 
followed by 9, and then by 4 and 10. In 59 per cent. of the 
45 pregnancies the foetuses numbered 5, 6 or 7. 
