1116 



SUBMAMMALIAN VERTEBRATES 



poults have ever been hatched from these. 

 Such poults have always been males and 

 so have the embryos that died but could be 

 sexed (Poole and Olsen, 1957) . The embryos 

 have the diploid chromosome number (Yao 

 and Olsen, 1955; Poole, 1959). Poole (1959) 

 has classified the possibilities whereby par- 

 thenogenetic turkeys with 2N chromosomes 

 could be formed as: (1) suppression of mei- 

 osis I or reentry of the first polar body fol- 

 lowed by reduction division; (2) suppres- 

 sion of meiosis II or reentry of the second 

 polar body; (3) nuclear but not cytoplasmic 

 division of the mature haploid ovum. 



The observation that all parthenogenetic 

 embryos from turkeys have been males 

 makes it probable that the explanation (1) 

 is not correct, because it would lead one to 

 expect some female offspring. In birds the 

 second polar body is not extruded until the 

 sperm penetrates the egg, so the second 

 mechanism is probably the correct one be- 

 cause the possibility for the two nuclei of 

 the ovum and the second polar body to fuse 

 would exist in this case. 



Linkage studies with males obtained from 

 parthenogenetic development are needed to 

 provide the answer whether possibly 2 or 

 3 is the correct one (Poole, 1959) . Attempts 

 to increase the incidence of parthenogenesis 

 have been made in order to find the possible 

 cause of parthenogenesis, and the following 

 factors have been mentioned as causes of 

 parthenogenesis. 



1. (31sen and Marsden ( 1953) suggested on 

 the basis of experiments in which turkey 

 hens were housed such that they could see 

 and hear or not see and hear turkey toms, 

 that sound and sight of other turkeys would 

 increase the incidence of parthenogenetic 

 development. The explanation was suggested 

 on the assumption that a neural mechanism 

 would cause the release of a pituitary hor- 

 mone involved in triggering parthenogenetic 

 changes in the oocyte. The hypothesis that 

 such a hormone might exist was founded on 

 evidence that LH injections and also "spon- 

 taneous" LH release cause maturation 

 changes in the nucleus of the ovum and 

 cause extrusion of the first polar body (Ol- 

 sen and Fraps, 1950) . Unfortunately, in the 

 experiments of Olsen and Marsden cited 

 above, the effect of sound and sight of other 



turkeys cannot be separated from the effect 

 of confinement in cages versus confinement 

 in larger pens and from the effect of artifi- 

 cial light versus natural daylight. In other 

 words, the effect assigned to sound and 

 sight of other turkeys might have been 

 caused also by differences in confinement or 

 differences in light. In a second experiment 

 by Olsen and Marsden (1956) the results 

 were reversed: birds that could hear and 

 see other males laid fewer eggs showing 

 more parthenogenetic development than 

 those hens that could not see, but might 

 have been able to hear the males. From 

 these experiments one might conclude that 

 environment may play a role in increasing 

 the incidence of parthenogenesis; however, 

 to determine which part of the environment 

 plays this role will require a better design 

 such as factorial designs. 



2. Olsen (1956) made the interesting ob- 

 servation that vaccination with fowl pox 

 vaccine increased the incidence of parthe- 

 nogenesis in a strain of turkeys in which 

 this trait already occurred. The mechanism 

 whereby this vaccine might act has not been 

 determined. 



During the period between hatching of 

 the chick and ovulation, many changes take 

 place in the follicle. The major change is the 

 deposition of yolk which occurs usually in 

 three phases. 



1. The phase of slow yolk deposition 

 which starts in the embryo and continues 

 for several months or years depending on 

 the species. During this period of yolk dep- 

 osition, the follicle is formed around the 

 vitelline membrane. 



2. The intermediate phase of yolk forma- 

 tion during which transparent vacuoles ap- 

 pear and during which yolk is formed in- 

 side the vacuoles (Marza and Marza, 1935) . 

 This phase lasts about 60 days. 



3. The phase of rapid yolk formation. 

 During this phase initially white yolk and 

 later yellow yolk is formed and the latebra 

 becomes distinguishable. This period starts 

 10 to 14 days before ovulation and ends at 

 ovulation. This phase is very rapid, and 

 yolk formation accounts almost entirely for 

 the enormous gain in weight which the 

 ovary undergoes during the 10 to 12 days 

 before ovulation starts. Data of Nalbandov 



