How do embryonic turtles process yolk? Evidence from the Snapping Turtle, <i>Chelydra serpentina</i> (Chelydridae)
Bibliographic record
Abstract
Compared with amphibians, oviparous reptiles and birds lay large eggs that contain abundant yolk. Because the yolk is extracellular, it must be taken up by cells of the yolk sac and metabolized so that products of yolk digestion can be transported to the embryo to fuel development. In birds, the yolk is processed by cells that line the inside of the yolk sac. A very different developmental pattern recently has been demonstrated in lizards and snakes in which the yolk sac cavity is converted to a compact mass of blood vessels lined by endodermal cells. In this study, we used scanning electron microscopy to determine which of these developmental patterns (if either) occurs in a representative chelonian, the North American Snapping Turtle (Chelydra serpentina (Linnaeus, 1758)). Our observations reveal that yolk-filled endodermal cells progressively fill the yolk sac cavity. These cells become organized around anastomosing blood vessels, forming elongated strands that are morphologically well suited for yolk digestion and vascular transport of nutrients. This developmental pattern shares features with that of squamates, but it differs markedly from that of birds. These observations indicate that mechanisms of yolk processing in lizards and snakes have an evolutionary history that pre-dates the squamate clade.
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How this classification was reachedexpand
Full frame machine prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. The Gemma side is a direct model label for every work in the frame, read from the title-only record. The Codex side is a classifier learned from the 10,348 direct Codex labels and calibrated to design-weighted sample rates; fields without enough sample support carry no Codex call. Candidate is the union of the two sides; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels.
Distilled classifier scores by category (both heads)
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.000 | 0.000 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.000 | 0.000 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.001 | 0.000 |
Machine scores (provisional)
The two teacher heads of the student model, read on this work. A score orders the frame for review; it never asserts a category, and the validation status ships verbatim with every row.
Baseline scores from an immature model (maturity gate not passed, 7 training rounds). Scores rank; they never assert a category.
score_only:v0-immature-baseline · verbatim from the scoring run: score_only means the number may rank works, and no category label ships from itClassification
machine, unvalidatedMachine predicted; a candidate call from one source (direct Gemma or distilled Codex), not a consensus.
How this classification was reached, model by model and score by score, is at the end of the page under "How this classification was reached".