A Guide to Aging of Pheasant Embryos' 



This paper presents a series of photographs illus- 

 trating the chronological sequence in the development 

 of pheasant ( Phasianus colchicus ) embryos as an aid 

 to identification of incubation stages of pheasant eggs 

 found in the field. The photographs are accompanied 

 by brief descriptions of the embryonic stages. The iden- 

 tifying criteria are based on prominent external charac- 

 teristics visible to the unaided eye. Dustman (1949), 

 Westerskov (1950), and Fant (1957) have described 

 various methods and criteria for identifying the stages 

 of embryonic development in the pheasant; this paper 

 supplements the findings of these workers. 



Pheasant eggs obtained from the Illinois State 

 Game Farm, Yorkville, were used in the investigation 

 on which this paper is based; the eggs were incubated 

 in a Buckeye incubator under standard incubating con- 

 ditions. Varying numbers of incubated eggs, but never 

 less than two eggs, were examined for each daily stage 

 of embryonic development; eggs were removed from the 

 incubator for examination at approximately the same 

 hour each day. Because some variation occurred in the 

 development of embryos in eggs incubated for the same 

 length of time, the embryo most closely representing 

 the mean degree of development was selected as typi- 

 cal for each particular stage. All data presented in this 

 paper were based on examination of fresh embryos. 



The cover photograph depicts a 13-day-old pheas- 

 ant embryo; it and all other photographs appearing in 

 this paper were taken by William E. Clark, Illinois Natu- 

 ral History Survey photographer. 



Prominent Embryo Characteristics 



In the photographs reproduced on the facing page, 

 embryos for days and 3-14 are shown in their natural 

 positions as they would be observed in decapped eggs. 

 Embryos for days 15-19, 21, and 22 are shown as they 

 would be viewed laterally with shells removed. Yolk 

 sacs were removed from the embryos for days 15-18 so 

 that embryo characteristics could be better observed. 



* A contribution from Illinois Federal Aid Project No. 30- 

 R, the Illinois Department of Conservation, the if. S. Bureau 

 of Sport Fisheries and Wildlife, and the Illinois Natural His- 

 tory Survey co-operating. 



TLabiskv is employed by the Illinois Department of Con- 

 servation under terms of the Federal Aid in Wildlife Restora- 

 tion Act and assigned to the Illinois Natural History Survey 

 for administrative and technical supervision. Opsahl was 

 formerly employed in this capacity; his present address is 

 Winona State College, Winona, Minnesota. 



Ronald F. Labisky and James F. Opsahif 



Prominent characteristics of embryos of various 

 ages (days old) are described below to supplement the 

 photographs. 



Day (unincubated): Germinal disc or blastoderm ap- 



pearing as an area 3-4 millimeters in diameter, 

 lighter in color than surrounding yolk surface. 



1 Day: Outer border of blastoderm appearing reticulate 



in contrast to the more central area; embryo (prim- 

 itive streak) not flexed and less than 4 milli- 

 meters in length; blood vessels not visible. 



2 Days: Blastoderm about 20 millimeters in diameter; 



embryo exceeding 4 millimeters in length; a 

 threadlike network of blood vessels encircling 

 embryo. 



3 Days: Embryo rather obscure, but flexed anteriorly; 



blood vessels evident in anterior portion of em- 

 bryo; heartbeat not apparent to unaided eye. 



4 Days: Entire embryo readily visible (lying on its left 



side), showing both anterior and posterior flex- 

 ures; network of blood vessels prominent; heart- 

 beat evident; limb buds, appearing as small 

 rounded swellings, barely discernible; eyes show- 

 ing no deposition of pigment; development of al- 

 lantois visible in umbilical region. 



5 Days: Embryo now a prominent "C" shape, with tail 



almost in contact with head; limb buds visible 

 as flaplike structures; eyes showing deposition 

 of dark pigment; allantois extending beyond lower 

 limb buds. 



6 Days: Pigmented region of eyes about 2 millimeters 



in diameter; limb buds appearing as distinct pro- 

 jections from body; cerebral hemispheres (fore- 

 brain) and midbrain lobes very prominent. 



7 Days: Pigmented region of eyes about 3 millimeters 



in diameter; limb buds expanded at distal ex- 

 tremities; cerebral hemispheres somewhat less 

 conspicuous, but midbrain lobes greatly ac- 

 centuated. 



8 Days: Pigmented region of eyes about 4 millimeters 



in diameter; limb buds showing no visible digita- 

 tion; midbrain lobes still prominent; upper man- 

 dible appearing as a slight protuberance. 



9 Days: Both cerebral hemispheres and midbrain lobes 



smaller in size relative to entire head, but mid- 

 brain lobes still prominent; toes evident, but not 

 separated; the wing alulae appearing as thumb- 



