1 



Perhaps the supplementary plates of certain species constitute an 

 exception, specifically- -D. bicornis Malewizkaja and D. facetus Gussew> 

 among which they have a completely different strilcture. 



is incepted last of any part of the armature and approximately in its final 

 location. In the beginning it has the shape of a straight or slightly bent, 

 transversely elongated thread, just as occurs in the early stages of the 

 development of the connecting plate of D. longicopula Bychowsky. 



In a number of species, further development takes place only 

 by means of the increase in dimensions of the supplementary plate without 

 any change in its shape, in other plates it takes place with a change in shape 

 and with unequal growth of separate sections of the plate. In order to avoid 

 numerous repetitions, let us analyze the development of the complexly 

 arranged supplementary plate in D. cornu Linstow (Fig. 146). After the 

 formation of the plate in the shape of the curved thread, it begins to thicken 

 and lengthen unequally in such a way that its middle part thickens much p. 146 



miore than the lateral ones. As a consequence, the supplementary 



plate acquires the shape of an isosceles triangle with a slightly invaginated 

 lower edge. Further, the growth develops mainly in three directions, 

 along the angles of the triangle, as a result of which is formed an inverted 

 T-shaped plate with slightly sharpened lateral edges and with a more blunt 

 upper edge which grows more intensively and soon the entire upper offshoot 

 appears with edges which are parallel or even slightly widened toward the 

 top lateral edges and a straight-cut upper edge. Approximately during this 

 time the lateral edges reach their final lengths and the middle of the lower 

 one, which was initially invaginated, begins to grow intensively forming a 

 small, more or less rounded space in the center and sonriewhat straightening 

 the line of the lateral growth and then forming two protuberances facing 

 downward. Continuing to grow, the top offshoot widens more and more at 

 its free end, which is divided, forming tvvo slightly concave lobes which 

 are characteristic of the final form of the plate. Somewhat back of the 

 upper offshoot grow protuberances of the lower edge forming two gro'Ai;hs 

 which are slightly narrowed to the free end and lie parallel and close to 

 each other. In such a fashion one can notice six stages of developmient: 

 the first, a transversely elongated straight plate, the second, a curved 

 stick-shaped plate, the third a triangle shape, the fourth an inverted T- 

 shaped plate with a widening of the upper stem, the fifth the appearance of 

 stems on the lower edge and finally the form corresponding to the connecting 

 plate of the adult D. cornu Linstow. The division into these stages is, of 

 course, arbitrary, their number can be decreased or perhaps more easily 

 increased. It is important, however, that the structure of similar ones 

 among the adult individuals of a great number of species of Dactylogyrus 

 corresponds to the enumerated stages of development of the supplementary 

 plate of D. cornu. As an example we will cite two species of Dactylogyrus 



155 



