DEVELOPMENT OF THE OPOSSUM 11 



3 in the 2-celled stage, 2 in the 4-celled stage, 2 in the 5-celled stage, 

 7 unfertilized, the remainder unaccounted for. 



No. 50. Placed with male February 1; removed male February 2; 

 replaced male February 5; killed February 10. 24 eggs: two 2-celled, 

 two 4-celled, 10 blastocysts of about 50 cells, 2 unfertilized, 8 unac- 

 counted for. 



No. 52. With male February 4 to 6 ; killed February 10. 25 young 

 (very small) eggs: one 4-celled stage; 3 in first cleavage; 14 unsegmented, 

 6 of which show pronuclei; the remainder unaccounted for. 



No. 54. Killed February 13. About 25 small eggs: one 2-celled 

 stage; one 4-celled stage; 2 in first cleavage; 11 undivided, of which 5 

 show pronuclei; 1 abnormal; 1 egg contained only shell and albumen, 

 the place of ovum being taken by a mass of epithelial cells. Other 

 eggs from this batch showed a number of epithelial cells from the 

 oviduct. The remainder lost and unaccounted for. 



No. 55. With male February 6; copulation probably February 7; 

 killed February 13. 22 eggs: all advanced, bilaminar blastocysts 0.8- 

 0.9 mm. in diameter, except 6 unfertilized eggs. 



No. 56. Killed February 14. About 20 eggs removed from the 

 Fallopian tubes, all devoid of albumen layer and shell; that is, just 

 as passed from the ovaries. 



No. 58. With male February 4; isolated February 8; killed Febru- 

 ary 15. Very young fresh corpora on ovary. Small, thin-shelled eggs, 

 all unsegmented and unfertilized, but normal and just passed into the 

 uterus. 



No. 76. Caught between January 13 and 15; killed January 16. 

 Both ovaries had discharged their follicles, but eggs were found in 

 only one oviduct. These eggs, 10 in number, were almost exactly 

 like those from No. 56. 



No. 81. Caught January 18 and killed next day. About 20 eggs: 

 all 4-celled with the exception of 3 or 4 unfertilized eggs. 



No. 82. Caught January 18 and killed next day. About 25 eggs: 

 almost fully formed bilaminar blastocysts with the exception of 6 

 unfertilized eggs. 



No. 83. Caught January 18 and killed next day. About 9 eggs: 

 1 unsegmented; four 4-celled stages exactly like those of No. 81; 3 

 blastocysts of about 50 cells, like those of Nos. 50 and 88. 



No. 85. Caught January 18 and killed the next day. About 25 

 eggs: one each in the following stages: 6, 7, 9, 10, 12, 14, 15, 17, and 

 18 cells; three of 8 cells; five of 16 cells and one abnormal egg. 



No. 88. Caught about January 18 and killed January 20. Number 

 of eggs not recorded, but 27 were sectioned and mounted, all young 

 blastocysts of 30-55 cells, except 6 abnormal eggs. 



No. 94. Killed January 21, several days after capture. A single 

 advanced bilaminar blastocyst, like those of Nos. 43, 55, and 82 was 

 taken. 



No. 112. Secured in December. February 11, successful lapa- 

 rotomy performed, corroborating previous diagnosis of pseudopreg- 



