Removal of Yolk from Oyster Eggs by Soxhlet Extraction for Clear Chromosome Preparations

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Abstract
The mature, spawned eggs of the American Eastern oyster, Crassostrea virginica Gmelin, contain yolk which interferes with the preparation of chromosomes and nuclear groups for the study of meiosis, fertilization, and karyology. Most samples of eggs cannot be studied cyto-genetically until the yolk is extracted. Simple and complete removal of all interfering yolky material can be efficiently accomplished, after Carnoy fixation in 3:1 alcohol-acetic acid, by extraction for 2 hr in a micro-Soxhlet apparatus with 1:1 mixture of chloroform and methyl alcohol. Standard orcein squashes can then be routinely made of these eggs hitherto considered refractory to clear staining of chromosomes. A thimble with a fritted glass end, pore size 40 [mu], is used as a receptacle for the eggs in the Soxhlet apparatus. After extraction the eggs can readily be washed off the fritted glass with the aceto-orcein staining solution. If the eggs are to be stored for some time prior to squashing and staining, 45-60% acetic acid or Carnoy''s alcohol-acetic acid 3:1 can be used for the storage fluid.