Journal of Okayama Medical Association
Published by Okayama Medical Association

Full-text articles are available 3 years after publication.


Miki, Yukiharu
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Both of Dicrocoelium dendriticum and Eurytrema pancreaticum belong to the family Dicrocoelidae. The miracidia of the former are indistinguishable from those of the latter. And as for the study of embryonic development of these miracidia it remains unknown, excepting only a few and brief reports about the miracidia of the former. The author studied these problems under the guidance of Prof. M. Suzuki. Prof. M. Suzuki has the opinion that in the embryonic development the arrangement of the divided cells are not cotyledonous. As to this observation, the author has endorsed the professor's excellent views. The author's careful and detailed studies about the embryonic development of these miracidia are summaried as follows: I. Concerning the embryonic development of the miracidium of the Dicrocoelium dendriticum. 1) The larger one of the two cells, which is produced by the first division of the eggcell begins to divide more and more, and 4-5 large cells so produced go to the inside of the eggshell, spreading their protoplasma. They cover the inside of the eggshell closely. And the author named this membrane, the first shellmembrane. And then 5-6 cells of the same type surround closely the body of the miracidium together after spreading their protoplasma in the similiar manner, except at the head and tail of the miracidium. After a little delay one cell goes to near both head and tail of the miracidium and covers the rest of the shellmembrane. Thus the three kinds of the shellmembrane are brought to completion. The author named them the 1st, 2nd and 3rd shellmembrane, 2) The smaller one of the two divided cells begins to devide a little later, but after the large cell has divided into 5-6 large cells, it begins to divide rapidly. And so in the morula period the total amount of the cells in addition to the large cells, reaches 35-36, in this period of the development, the large cells organize the epidermis of the miracidium, and one large cell exists in every three parts of the boby, the head, the centrum of the body and the tail individually. The remaining parts of the body are filled with small cells, an the above described 35-36 cells answer the purpose of organ foundation. 3) The Epidermis of the miracidium consists of the 8 large cells, which are situated in a definite arrangement, and upon the surface of the epidermis the countless cilia come to existence. Just under this epidermis, there is a subcutaneous layer. 4) on the surface of the above described 8 cells is situated an extraordinarily thin and transparent cuticula. This cuticula is not due to a definite cell, but is produced by a change in the external surface of the epidermis into cuticula. 5) This miracidium has two kinds of subcutaneous muscle, the one is longitudinal muscle fiber and the other is horizontal muscle fiber. The development of the former is remarkably primitive, but the lattter, especially the sphincterial muscle in the middle part of the miracidium, developes well. These mucle fibers come to existence from the small type of cells. 6) The four large cells form the intestine of the miracidium situated on the anterior part of the miracidium, but it is a rudimentary organ, because no one can investigate the food in it. Afterwards these four cells turn into so called syncytium. The comleted intestine is a rectangle and never represents an isosceles triangle as seen in the miracidium of Eurytrema pancreaticum. 7) Before the intestine building, the stingdrawer is completed. The muscle is made from the small cells, which existed in the organ foundation in the middle part of the body and makes a thin muscle layer along the both side of the intestinal wall. The anterior end of the mucle fiber goes to the anterior subctaneous layer of the miracidium. The posterior end connects to the nervous cell group. 8) The central nervous system is made from the deeply stained small cells, which exist in the equator part of the miracidium in the morula period, 1-2 of the cells exist each, just near the ventral side and afterwards each cellgroucp onnects by sending out nervous fiber. Thus the shape of the nervous system just resembles a dump-bell, and it sends out 6 nervous trunks. 9) The excretory vesicle is characteristic in this miracidium, which is seen at the posterior part of the mature miracidium as a long ellipse. In spite of the views of Leukart, Henkel and Mattes who regared this organ as a germ cell, the author's observation obtained quite different results. The author studied the detailed structure and obtained the following result. The excretory vesicle is made from 2 large cells each having an excretory duct and excretory pore. And these contain granules with quite the same size and structure. These points are suffcient to decide with firm confidence that this organ is an excretory vesicle. The flame cells situated at each side of the central nervous systems. And the detailed development of it as well as the excretory duct are all beyond observation, because of their extraordinary minuteness. 10) The germ cell makes its characteristic appearance in the early period of development. The germ cell is made from two large cells, and according to the progress of the development come to the syncyticum in deeply stained. II. Concerning the embryonic development of the miracidium of the Eurytrema Pancreaticum : About the development of the this miracidium it is quite identical with that of the former, except for a few points described below. 1) The from of the eggshell is shorter and large in comparison with that of the Dicrocnelium dendriticum and the ratio of the longer axis of the egg to the shorter one is 1:1.3-15, while it is 1:1.9-2.2 in the case of Dicrocoelium dendriticum. The intestine is also larger, representing an isosceles triangle and is of crown form through the peculiar ring muscle fiber on the head of the intestine. The longer axis of the excretory vesicle runs at an angle of 35°-45° to that of the egg, instead of paralell as in the case of the Dicrocoelium dendriticum. 2) In the mature miracidium of this worm, the epidermis cells of the tails melt in Karyolysis. The ring muscle of head cosists of two small cells. This is the characteristic point of this miracidium and is helpful to distinguish this mircidium from that of Dicrocoelium dendriticum.