. Zoology : for students and general readers . Zoology. LIFE HISTOBT OF FLUKE-WORMS. 149 about in its place and secreting a slime, a cyst is gradually formed, with a spherical shell. This constitutes the " pupa " state of the Oercaria. Steenstrup thinks that the Cercaria casts a thin skin. In this state the body can be seen through the shell of the cyst, as in Fig. 98, C, where the circle of spines embedded around the mouth is seen. The encysted OercariEe remain in this state from July and August until the following spring ; and during the winter months, in snails kept in warm rooms,
. Zoology : for students and general readers . Zoology. LIFE HISTOBT OF FLUKE-WORMS. 149 about in its place and secreting a slime, a cyst is gradually formed, with a spherical shell. This constitutes the " pupa " state of the Oercaria. Steenstrup thinks that the Cercaria casts a thin skin. In this state the body can be seen through the shell of the cyst, as in Fig. 98, C, where the circle of spines embedded around the mouth is seen. The encysted OercariEe remain in this state from July and August until the following spring ; and during the winter months, in snails kept in warm rooms, they change into Distomas (Fig. 98, D), the mature fluke differing, however, in some im- portant respects from the tailless larvse. In nature they remain from two to nine months in the encysted state. " Now," asks Steenstrup, " whence come the Cercariae ?" Bojanus states that he saw this species swarming out from the "king's yellow worms," which are about two lines long and occur in great numbers in the interior of snails. From these are developed the larval Distomes, and Steenstrup calls them the " nurses " of the Cercarise and Distomes. They exactly resemble the "parent-nurses" (Fig. 98, A, and 100), and, like them, the cavity of the body is filled with young, which develop from egg-like balls of cells. Steenstrup was forced to conclude that these nurses originated from the first nurses (Fig. 98), which he therefore calls " ; Here the direct observations of Steenstrup on the Cercaria echmata came to an end, but he believed that the parent- nurses came from eggs. The link in the cycle of generations he supplied from the observations of Siebold, who saw a Cercaria-like young (Fig. 99, B) expelled from the body of the ciliated larva of Monostomum niuta- lile: Steenstrup remarks that " the first form of this embryo is not un- like that of the common ciliated pro- geny of the Trematoda, as they have be
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Keywords: ., bookcentury1800, bookdecade1870, booksubjectzoology, bookyear1879
