Embryonic development of the platyfish (Platypoecilus), the swordtail (Xiphophorus), and their hybrids. Bulletin of the AMNH ; v. 94, article 4

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New York : [American Museum of Natural History]
"One. Embryonic development of the viviparous poeciliid fish Platypoecilus maculatus may be conveniently divided into 26 stages for descriptive purposes. 2. The embryonic growth rate for P. maculatus is determined by comparison of morphological age (in terms of embryonic stage) with theoretical age (days after the birth of a previous brood). This comparison is based on a series of embryonic broods obtained by laparotomy at various times during the twenty-eight- to thirty-day reproductive cycle of this species. 3. A study of growth and organogenesis in P. maculatus reveals the following features: A. The concomitant regression of the extra-embryonic membranes and the yolk mass is accompanied by a drop in the slope of the growth curve. B. The initial formation of the extra-embryonic membranes takes place in a manner similar to that in the 'amniotes.' C. Cleavage, gastrulation, and neurulation follow a course basically similar to that of other teleosts. D. Blastopore closure occurs after tail bud formation. E. The notochord forms directly from endoderm by delamination. F. Pigment formation is evident first in the retina and subsequently in the choroid and meningeal coats. G. Kupffer's vesicle (post-anal gut) contributes to the development of the urinary bladder. H. The formation of the ventral aorta and aortic arches is described with regard to the reversal of blood flow in the ventral aorta and the change of position of the sinus venosus during yolk regression. 4. Comparisons with other species of Platypoecilus (P. variatus, couchianus, and xiphidium) reveal no significant differences in embryonic development. 5. Platypoecilus maculatus development, compared to that of Xiphophorus hellerii and Platypoecilus-Xiphophorus hybrids, shows the following differences: A. Initial pigment differentiation in Xiphophorus occurs one stage later than in Platypoecilus. The hybrids form pigment at the same stage as Platypoecilus or earlier. B. Over the same period of time, Xiphophorus embryos attain a larger size than Platypoecilus embryos. The growth rates of the hybrids all coincide with or exceed those of Xiphophorus. C. Caudal fin differentiation is one stage later in Xiphophorus than in Platypoecilus. However, all the hybrids form a caudal fin at the same rate as P. maculatus, and the F[subscript 1] X Platypoecilus backcross hybrid embryos exceed both parental species in this respect. 6. Sterility and embryonic anomalies are frequent among hybrid females. This is particularly true of F[subscript 1] females possessing the Sd (spotted dorsal fin) character, indicating a linkage of lethal factors with this pattern gene"--P. 226.
p. 165-229 : ill. ; 27 cm.
Thesis (Ph. D.)--New York University.
Includes bibliographical references (p. 227-229).