TABLE 1.
Stages of Engystomops development
| Stage1 |
Characteristics of embryos | Age2 in: | |||
|---|---|---|---|---|---|
| E | X | G | Hours | Days | |
| 1 | 1 | 1 | Fertilization (Fig. 1A). | 0.0 | |
| 2 | 2 | 3 | Two cell stage. | 0,3 | |
| 3 | 3 | 4 | Four cell stage (Fig. 1B). | 0,6 | |
| 4 | 4 | 5 | Eight cell stage (Fig. 1C). | 1 | |
| 5 | 5 | 6 | Sixteen cell stage (Fig. 1D, 3A). | 1,3 | |
| 6 | 6 | 7 | Thirty-two cell stage (Fig. 1E). | 1,7 | |
| 7 | 7 | 8 | Large-cell blastula (Fig. 1F,3B). | 3 | |
| 8 | 8 | - | Medium-cell blastula (Fig. 1G, 3C–D). | 5 | |
| 9 | 9 | 9 | Advanced blastula. | 7,2 | |
| 10 | 10 | 10 | Early gastrula. Embryos develop the dorsal blastopore lip (Fig. 1H,3E–G). | 11,5 | |
| 11 | 11 | 11 | Mid gastrula with a large yolk plug that measures about one-half of the embryo’s diameter (Fig. 1I). | 16,2 | |
| 12 | 12 | 12 | Late gastrula. The yolk plug measures one- third of the embryo’s diameter or less (Fig. 1J–K, 3J–K, M). | 19,7 | |
| 13 | 13 | 13 | Slit blastopore stage. Some embryos have a small blastopore (Fig. 1L,3L). The neural plate becomes visible in the late stage 13 (Fig. 3N). | 1 | |
| 14 | 14 | 14 | Early neural fold stage (Fig. 1M, 3O, 4A). | 1.1 | |
| 15 | 15 | Mid neural fold stage (Fig. 1N–O, 4B–H). | 1.2 | ||
| 16 | 16 | Closure of the neural tube (Fig. 1P, 4I–L). | 1.3 | ||
| 17 | 17 | Tail bud stage. The tail bud and the head region protrude beyond the yolky endoderm (Fig. 2A, 5A–F). | 1.5 | ||
| 18 | 18 | Muscular activity. The branchial arches protrude on the sides of the head. The cement gland is visible. The tail becomes elongated (Fig. 2B–C, 5G–H) | 2 | ||
| 19 | 19 | The heart beats, and the gill buds develop (not shown). | 2.3 | ||
| 20 | 20 | Circulation to the external gills. The first gill pair has 3 branches at this stage. Buds of the second gill pair are visible (Fig. 2D). | 2.5 | ||
| 21 | 21 | The first gill pair has 4 branches, and the second gill pair has 3 branches (not shown). | 2.8 | ||
| 22 | 22 | Blood circulation in the tail fin is detected. Five branches occur in the first pair of external gills, and 4 branches in the second pair. Embryos have a tadpole appearance (Fig. 2E). | 3.1 | ||
| 23 | 23 | The external gills have reached their full size. There are 6 gill branches in the first pair and 5 branches in the second pair of external gills. The opercular fold is forming. Embryos have a white appearance, although they contain some dark pigment (Fig. 2F–G). | 3.4 | ||
1
The stages of development for Engystomops (E) are compared to the table of stages of X. laevis (X) (Nieuwkoop and Faber, 1994), and to the general staging table for frogs (G) (Gosner, 1960).
2
Developmental times for E. coloradorum embryos maintained at room temperature (18–23°C) in a humid chamber.