. The Biological bulletin. Biology; Zoology; Biology; Marine Biology. OVULATION, OVA, AND KMBRVOS OF MVSTKIA'S 483 Incidental observation by the writer in 1946 showed that two eggs of the skate. Raia crinacca, spawned on July 13 or 14 in the aquarium of Dr. F. A. Hartmann and kindly contributed by him. were in open neural fold stages on July 21. Neural folds fused and embryos elongated from 3 to 5 mm. at the rate of about mm. per day over a period of 3% days and moved laterally by rhythmic contraction of somite-. Unfortunately accidental injury to the egg-cases resulted in the death of the
. The Biological bulletin. Biology; Zoology; Biology; Marine Biology. OVULATION, OVA, AND KMBRVOS OF MVSTKIA'S 483 Incidental observation by the writer in 1946 showed that two eggs of the skate. Raia crinacca, spawned on July 13 or 14 in the aquarium of Dr. F. A. Hartmann and kindly contributed by him. were in open neural fold stages on July 21. Neural folds fused and embryos elongated from 3 to 5 mm. at the rate of about mm. per day over a period of 3% days and moved laterally by rhythmic contraction of somite-. Unfortunately accidental injury to the egg-cases resulted in the death of the ;. FIGURE 8. Rate of development of living embryos of M. canis. Labels indicate the orienta- tion of ova in utero. Eggs in egg-cases were placed on wet cotton in covered finger bowls set in running sea water at 22-23° C. Clark (1926), at the Plymouth Laboratory, opened egg capsules of R. brac/iyn>\i tagged at the time of spawning and found cleavage stages through the fourth day of incubation. His next report is that of an early neural fold stage, aged 24 day>. while embryos of 4 to mm. were observed after 35 and 43 days. Clark's series is incomplete with no data for embryos between and mm. nor did he follow the development of individual eggs. The exceedingly slow rate in R. brachyura as compared with that of other elasmobranchs mentioned above may be a species difference and may be attributed in part to the low temperature of the laboratory tanks at Plymouth (° C.). On the basis of the above data on the development of individual eggs of -17. canis, together with the marked difference in stage and arrangement in sequence of the embryos in a uterine series, it can be estimated that successive ovulations usually of two eggs, occur in this species about every 30 to 40 hours. This is a reasonable estimate in view of Clark's (1922) observation of a 24 hour interval between spawnings in R. brachyitra but it is an approximation only. More data
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Keywords: ., bookauthorlilliefrankrat, booksubjectbiology, booksubjectzoology
