DEVELOPMENT OF HALF-EGGS OF CHAETOPTERUS PERGAMENTACEUS WITH SPECIAL REFERENCE TO PARTHENOGENETIC MEROGONY

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Abstract
The unfertilized Chaetopterus egg (94 [mu]) may be stratified and broken into unequal halves of a uniform size by a centrifugal force of 10,000 X g for 5 min. The nucleate white halves (83 [mu]) contain oil, clear layer, mitochondria and a little yolk; the non-nucleate yellow halves (64 [mu]) contain only yolk. The centrifuged whole egg, both fertilized and parthenogenetic, may develop similarly to the uncentrifuged egg. The white halves, both fertilized and parthenogenetic, may cleave according to the typical annelid pattern; but there is a tendency toward equal first cleavage and amoeboid form and later development with irregular cells and large nuclei. The blastulae tend to fuse together. The yellow halves, both fertilized (= fertilized merogone) and parthenogenetic ( = parthenogenetic merogone) usually lift off a characteristic fluted fertilization membrane and pass through only one cleavage, and become amoeboid. Parthenogenetic merogony (== development without nuclei) takes place in Chaetopterus, an annelid, as well as in sea urchins, but development does not go as far.