. The Biological bulletin. Biology; Zoology; Biology; Marine Biology. REPRODUCTION IN PHORONOPSIS VIRIDIS 185 ANNUAL CYCLE IN THE GONADS The developmental sequence in the gonad of Phoronopsis viridis is very similar to that described for Phoronis ijiuiai and Phoronis austral is by Ikeda (1903) and for Phoronis psammophila by de Selys Longchamps (1907). Female Gonad. The breeding season for Ph. viridis lasts throughout most of March and April. In the case of the female, the gonad in late February contains large numbers of full-sized ova, each about 60 p. in diameter. At this time most of the ov
. The Biological bulletin. Biology; Zoology; Biology; Marine Biology. REPRODUCTION IN PHORONOPSIS VIRIDIS 185 ANNUAL CYCLE IN THE GONADS The developmental sequence in the gonad of Phoronopsis viridis is very similar to that described for Phoronis ijiuiai and Phoronis austral is by Ikeda (1903) and for Phoronis psammophila by de Selys Longchamps (1907). Female Gonad. The breeding season for Ph. viridis lasts throughout most of March and April. In the case of the female, the gonad in late February contains large numbers of full-sized ova, each about 60 p. in diameter. At this time most of the ova still possess the large germinal vesicle. They may be packed very closely and each is covered by a thin, squamous epithelium, one cell thick. The remnants of the vasoperitoneal tissue take the form of small patches or strands of granular cytoplasm between the masses of ova. By about the middle of March many of the. ova have become freed of the invest- ing membrane. As this happens the germinal vesicle breaks down and the first maturation division begins. This division proceeds to first metaphase and stops (Fig. 4). The female nucleus remains at this stage until the egg is shed from the. mn FIGURE 4. Camera lucida drawing of an ovum from the body cavity. The female nucleus is in metaphase. From a female collected in March, fn—female nucleus, mn—male nucleus. body. Once the ovum is freed of its investing epithelium it moves toward the periphery of the body and in the space between the outer surface of the gonad and the body wall the ripe ova collect. Occasionally an ovum will proceed to divide while still in the body cavity. Up to three or four such embryos have been found in one adult. Those found have always been blastulae. Similar embryos have been seen by de Selys Longchamps (1907) in Phoronis mulleri and Phoronis sabatieri. Throughout the months of March and April large numbers of ova ripen and become free in the body cavity, where fertilization takes place. By the end
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Keywords: ., bookauthorlilliefrankrat, booksubjectbiology, booksubjectzoology
