8o BIOLOGY OF THE LABORATORY MOUSE 



Corpora lutea. — Following ovulation, the ruptured follicles, and occa- 

 sionally also large unruptured follicles (83) undergo changes which trans- 

 form them into corpora lutea. During the first few days of its development 

 each young corpus passes through characteristic stages from which an 

 approximate though probably not very accurate estimate of its age is 

 possible (38, 39, 128. See also p. 151). The subsequent history of the 

 corpus depends on the sexual history of the animal. On the basis of this 

 history, four types of corpora may be distinguished. The following descrip- 

 tion of these, except as otherwise noted, is based on the observations of 

 Long and Evans (83) on corpora lutea in the rat. 



1. Corpora lutea of ovulation are corpora formed during an ordinary 

 estrous cycle where mating does not occur, or at a postpartum estrus if 

 mating or lactation do not occur. Such corpora may persist with little 

 obvious degeneration through two, three, or four cycles in the mouse (3), 

 possibly longer in the rat, so that an ovary from a mouse which has run 

 several uninterrupted cycles often contains as many as sixteen large, well 

 defined corpora. The youngest set is distinguished not only by the mor- 

 phological characteristics which set it apart for the first one or two days 

 but also by the fact that it stains blue with hematoxylin (3). Older sets 

 have a greater affinity for eosin. Perhaps a more critical test is a change 

 in certain lipoid droplets which can be detected in the luteal cells following 

 appropriate fixation. These are small and regular in size in young corpora, 

 become larger and less regular in size with the onset of the next estrus. 

 Long and Evans {d>T^) believe that the functional life of the corpus has 

 terminated by the time the changes in the droplets appear. Another test 

 of age is provided by the fact that the lutein cells of old corpora stain more 

 readily than those of young ones with the vital dye Dianil Blue 2R injected 

 intraperitoneally. 



2. Corpora lutea of pseudo pregnancy are corpora lutea formed following 

 a sterile mating. Such a mating induces a diestrous interval of some eight 

 or ten days, and throughout this interval the lipoid droplets in the newly 

 formed corpora retain the small, uniform size characteristic of young cor- 

 pora of ovulation. Corpora of pseudopregnancy become more highly 

 vascularized (39) and attain a slightly larger size than do corpora of ovu- 

 lation. There is evidence that the prolonged diestrus following sterile 

 mating is caused by a lengthened functional life in the corpora of 

 pseudopregnancy . 



J. Corpora lutea of pregnancy are corpora formed following a fertile 

 mating. For the first few days these cannot be distinguished from corpora 



