Artifactual and Natural Aberrations Among 

 Eggs in Sebastodes 



Certain embryonic stages were consider- 

 ably distorted by the formalin used in preser- 

 vation. Many eggs containing embryonic stages 

 II through V were larger than others from 

 the same ovary, although the embryos in the 

 size groups of eggs appeared identical (table 

 6, fig. 4). This condition appeared to be 

 caused by the rupturing of the yolk mem- 

 brane, owing to the osmotic effects of the 

 preservative, whereas the egg membrane re- 

 mained intact. From 25 to 39 percent of the 



Table 6. — Sebastode s paualsplnls — embryonic stage, egg diameter, and 

 embryos per gram of ovary 



20 



15 



10 



>- 5 

 o 



z 



UJ 



S 

 q: 



^ 



20 



10 



(A) STAGES n-2 



oLA 



0.70 080 Q90 1.00 1.10 1.20 



EGG DIAMETER (EXCLUDING EMBRYO) IN MILLIMETERS 



Figure 4. — Diameter frequencies of fertilized eggs from 

 the ovaries of Sebastodes paucisplnls showing the effect 

 of formalin preservation before (A) and after (B) 

 blastopore closure. 



stage II to V eggs were affected in fish con- 

 taining these stages. None of the eggs of 

 stages VI to XI were affected. It may be 

 relevant that blastopore closure takes place 

 at stage V, The greater fragility of early- 

 stage eggs has been observed in other fish 

 species (Ahlstrom and Ball, 1954). 



Another type of aberrant Sebastodes egg in 

 ovaries containing embryos consisted of un- 

 fertilized or undeveloped eggs of the same 

 original batch as the developing embryos. 

 These eggs contained a ruptured yolk mem- 

 brane, had yolk material of uniform texture 

 distributed within the egg membrane, had a 

 normal oil globule, and were 1.20 to 1.84 mm. 

 in dianneter..A pooled sample of embryos from 

 several specimens of S. paucispinis contained 

 23,146 embryos and 14 (0.06 percent) unferti- 

 lized or undeveloped eggs. These eggs were 

 found in all species that contained embryos. 



Formalin may also cause swelling in ripe, 

 unfertilized eggs. The diameters of intact, 

 ripe, unfertilized eggs of most of the species, 

 of Sebastodes averaged about 0.80 mm. Those 

 of S. rosaceus were smaller- -average about 

 0.65 mm. The female S. serriceps contained 

 a group of eggs that averaged 0.94 mm. and 

 were 0.86 to 1.00 mm. in diameter- -the 

 largest unfertilized eggs found in any of the 

 specimens. Because no other comparable ma- 

 terial for this species appeared in the collec- 

 tions, the amount of possible swelling caused 

 by preservation is not known. 



The diameters of the yolks of newly fertil- 

 ized eggs and stage X embryos are closely 

 similar (except as affected by preservation 

 artifacts). One specimen of S. ovalis con- 

 tained unfertilized eggs that averaged 0.91 

 mm. and were 0.80 to 0.96 mm. in diameter 

 (fig. 5C). Most of these, except for a few 

 0.80 to 0.84 mm. in diameter, seemed to have 

 ruptured yolk membranes, although this con- 

 dition is difficult to detect because of the 

 darkness of the yolk material in unfertilized 

 eggs preserved in formalin. In another speci- 

 men of S. ovalis containing stage X embryos 

 the dianneter of the area enclosed by the yolk 

 membrane averaged 0.80 mm. and ranged 

 from 0.72 to 0.88 mm. (fig. 5A-D). 



To study the relation between yolk size of 

 embryos, I determined the number of em- 

 bryos per gram of ovary and measured the 

 diameters of eggs for the various embryonic 

 stages in the ovaries of the nine specimens 

 of S. paucispinis. The thickness of the embryo 

 was not included in the egg diameter, and as 

 the perivitelline space is not developed, the 

 "intact yolk" egg diameters are, for practical 

 purposes, also yolk diameters. (Stage XI 

 embryos, which have oval yolks, are difficult 

 to measure accurately.) The volume enclosed 

 by the yolk membrane did not decrease as 

 the embryos increased in size (table 6). This 

 fact is also shown by the decrease in em- 

 bryos per gram of ovary as the embryos 



