ARTinCIAL PARTHENOGENESIS 



185 



CONDITION 



NUMBER & PERCENTAGE 



2. Rate of cleavage. This observation will have value only if the temperature for 

 the experimentals and controls is identical. 



3. Analysis of haploid characteristics of the tadpoles which develop. These include 

 microcephaly (due to sluggish or incomplete gastrulation); dorsal flexion of head 

 and tail; increased number of cells per unit area (except the notochord); and fre- 

 quent oedema which is thought to be due to the malfunctioning of the excretory 

 system of haploid tadpoles. Oedema alone is not an adequate criterion for there 

 are many environmental factors which will cause this condition in normally dip- 

 loid tadpoles. 



4. Fix and stain tail tips of parthenogenetic tadpoles 9 to 10 days old to make chro- 

 mosome counts. (See under Tail Tip Technique. ) 



Many of the parthenogenetically activated eggs will proceed to early stages of development 

 and then cytolyze. It would be instructive to make a rapid preparation of a healthy neurula 

 stage to determine whether the cells are truly haploid, using the method of Tyler (1946). 

 This simply involves placing the neurula on a coverslip; separating or teasing apart its 

 cells in a minimum amount of culture medium, possibly with the aid of 0. 1% KOH; invert- 

 ing the coverslip over a second coverslip on which is placed a large drop of Bouin's fixa- 

 tive. The edges of the upper coverslip should cross the corners of the lower coverslip so 

 that they can be separated the more easily after fixation. If the coverslips are moved 

 over each other slightly, this will separate the cells of the neurula and they will become 

 fixed and most of them will become attached to one of the coverslips. After 5 minutes, 

 place the paired coverslips in a Syracuse dish of Bouin's fluid and gently tease them apart 

 with needles. Allow the fixative to act another 5 minutes. From this point on the cover- 

 slips may be treated as any mounted cytological preparation, and may be stained for chro- 

 mosomes. It should be possible to locate some mitotic figures in the neural crest cells 

 which will answer the question relative to ploidy. 



In general the frog's egg lends itself admirably to this type of experiment. The results 

 should give from 0% to 18% cleavages, with the average about 6%. The eggs which show 

 relatively normal cleavages should be isolated and given special care in the hope that 

 some may develop into tadpoles. 



