. The Biological bulletin. Biology; Zoology; Biology; Marine Biology. 192 M SHIRAE ET AL. am am .. Figure 6. The rejection type of Sympli^inn IV/>MJ» that is initiated before fusion of ampullae. (A) View of allorejection under stereomicroscope. Ampullae of two incompatible colonies make contact at their growing edges, and infiltrated hemocytes (arrowheads) are observed at the tips of ampullae. (B) Contact area of two incompatible colonies. Arrows indicate the contact point of these two colonies. Many hemocytes infiltrate the tunic and disintegrate, and the surrounding tunic is broken, am. a
. The Biological bulletin. Biology; Zoology; Biology; Marine Biology. 192 M SHIRAE ET AL. am am .. Figure 6. The rejection type of Sympli^inn IV/>MJ» that is initiated before fusion of ampullae. (A) View of allorejection under stereomicroscope. Ampullae of two incompatible colonies make contact at their growing edges, and infiltrated hemocytes (arrowheads) are observed at the tips of ampullae. (B) Contact area of two incompatible colonies. Arrows indicate the contact point of these two colonies. Many hemocytes infiltrate the tunic and disintegrate, and the surrounding tunic is broken, am. ampulla; I. tunic. Bars: A = 200 /urn: B = 50 /j,m. recruiting cells from the circulating blood. Furthermore. 3 to 4 h after the stoppage of blood flow, phagocytes engulfed other hemocytes or hemocyte clusters in the rejection areas of blood vessels (Fig. 4C). The hemocyte clusters were encapsulated by phagocytes (Fig. 4D), and the encapsulated clusters sometimes attained a diameter of about 50 juin. All types of hemocytes, including MCs. were engulfed or en- capsulated by phagocytes. In the allorejection reaction of other botryllids. MCs always infiltrate the tunic from the blood vessels and disintegrate, but in the allorejection reac- tion of B. scalarix, MCs showed neither infiltration nor disintegration; they also did not show any morphological change inside the blood vessels (Fig. 5). Allorejection reactions in Symplegma reptans In botryllid ascidians the ampullae exhibit tip-to-side fusion after extension into the facing colony (Katow and Watanabe, 1980). In S. reptans, the fusion process in auto- geneic and syngeneic colony pairs has been reported (Mukai and Watanabe, 1974) as tip-to-tip fusion: ampullae of the two colonies did not extend into the facing colony and the ampullae of both colonies came into contact with each other at their tips. But as far as we observed, tip-to-side fusion of ampullae always occurred in the fusion reaction of S. reptans, as in botryllid as
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