1 



Judging by the head end, by the structure of the edge hooks, and by the 

 location of the middle hooks of the larva, the latter became attached to 

 the host and lost its ciliary epithelium very recently. 



lateral hooks takes place rather slowly so that the middle hooks succeed 

 in growing almost up to their final dimensions during the same period, 

 (Table 3). The location of the edge hooks of the youngest larva is charac- p. 149 

 teristic: the hooks are located along the edge of the disc (with the exception 

 of the 7th pair lying almost in the center of the disc), and the hooks of the 

 6th pair are separated from each other somewhat further than from the 

 others and are oriented with their terminal hooks toward each other 

 locating themselves in such a way and in the same place as the middle 

 hooks will be located subsequently. The latter are already present but are 

 located above the center of the disc (with the upper edge even extending 

 beyond it. Fig. 148, A). As we had supposed in 1936, they already have a 

 characteristic shape with the "displacement" between the basal part and the 

 point. The point is already of final length but is still thin and frail, just 

 as the base part, represented by a straight little stick two times smaller 

 than the hook part, which is also frail and thin. The connecting plate also 

 exists in the shape of a straight or slightly curved thread only a little 

 shorter than the middle hooks. It lies freely between the middle hooks. 

 Very soon after the stage described, the middle hooks descend to the lower 

 edge of the disc, displace the 6th pair of edge little hooks laterally and cut 

 through, thus assuming their final position. At this time, their base part 

 is already one and one -half to two times longer than the tip of the hook 

 (Fig. 148, C). Further development of the middle hooks of Dogielius 

 (Fig. 149, A) takes place just as among Dactylogyrus by way of the thicken- 

 ing of the parts which were incepted earlier and the accretion of the basal 

 part at its free end and then the widening of the free ends and the formation 

 of the interior and exterior extensions which almost merge and form, so 

 to speak, a widened triangular plate. The growth of the connecting plate p. 150 



(Fig. 149, B) parallels the growth of the middle hooks, reaches its final 

 length rather slowly and begins to thicken in proportion with its final shape. 

 The development of internal organs takes place in the same way as among 

 Dactylogyrus. The copulatory organ (Fig. 150) is incepted at the time when 

 formation of the widening corresponding to the extensions of the middle 

 hooks has already begun. At first it has the shape of a thin, almost straight p. 151 

 pipe with a weakly developed base from which departs the supporting appa- 

 ratus in the shape of a band with a small widening in its upper third and 

 with a sharpened free end. Further growth takes place rather quickly by way 

 the shape of an increase in the volume and size of the pipe and of the base 

 and of the growth and complexity of the terrainal and of the supporting 

 apparatus. The copulatory organ acquires its final forna at the same time 

 as the termination of the growth of the parts of the attaching armature. 



160 



