ユウシホガヒ <i>Tellina juvenilis</i> H<sub>ANLEY</sub> の發生に就て

Abstract

Tellina, juvenilis is a small vivalve having thin shells, pink or, white in colour. In the vicinity of the Kanazawa Laboratory, it is found abundantly above the low tide mark on the sandy bottom containing a slight admixture of mud and humus. Its breeding occurs mostly in early summer. The sexual elements are spawned out through the exhalent siphon which is extended to such a length as four or five times that of the shell. As the eggs or sperms are accumulated in the siphon, they are expelled forcibly by sudden whip-like lashing of the organ. The egg measures 134-155μ in diameter having a gelatinous coating 23-55μ in thich-ness. This remarkable coating is formed in the ovary. it is readily demonstrable by using a fluid of neutral red. There is also a distinct vitelline membrane of fine reticular structure-The diameter of the vitelline space is ca. 103μ and that of the yolk ca. 62μ, so that the perivitelline space is very wide. And the yolk is freely shifted in the space by the pushing force of the spermatozoon which penetrates into there and its head is attached to the surface of the yolk. When eggs are shed the germinal vesicle has already disappeared and the first polar spindle is formed. During the early segmentation of the egg there protrude no polar lobes. The embryo attains to the shelled-larva-stage in about 26 hours at 23°C. Apical cilia are present. The reddish-purple colouration along the, umbonal region, and the projected anterior margin of the shell, in grown veliger are characteristic to the species as shown in figures.