340 University of California Publications in Zoology [Vol. 19 



Because of this increase in length, the posterior end is often doubled 

 back in the egg. The primitive digestive tract is larger and the germ 

 balls are more conspicuous. For the first time the cilia on the surface 

 of the body are clearly distinguished. The activity now is often 

 violent, the miracidium lunging back and forth against the operculum. 

 The egg is now ready to hatch. Figure 16 shows another mature 

 miracidium also ready to hatch, in which the central nervous system 

 is apparent. 



I am inclined to believe that studies on the development of other 

 echinostomes will show the above description of development to be 

 characteristic of the family. Because of the opaque condition I was 

 unable to determine whether the two flame cells are joined by short, 

 nearly straight capillaries or if the capillaries are long and much coiled. 

 The excretory pores are located on each side near the posterior end. 

 The excretory system of most miracidia seems to consist of but two 

 flame cells and two capillaries. Looss (1896, pis. XI and XII) finds 

 the excretory system of the miracidium of Gastrodiscus acgyptiacus 

 (Cobbold), Gastrothylaa gregarius Looss, and "Distomum hepaticum 

 variet. aegyptica,'' following this plan. Looss (1892, pi. XLX) again 

 shows that in " Amphistomum subclavatum," the excretory system 

 consists of but two flame cells and two capillaries. 



A few minutes after figure 15 had been drawn, I was fortunate 

 enough to observe the miracidium escaping from the egg. After many 

 and vigorous lunges the operculum opened as if on a hinge (fig. 17). 

 Within three seconds the whole miracidium was out and swimming 

 vigorously about in search of its proper host. The operculum measures 

 0.023 mm. in diameter. Inside the newly hatched egg (fig. 17) is to 

 be seen a considerable amount of waste and oily material. This 

 material as well as the operculum is lost, however, inside of a few 

 hours (figs. 18 and 18a). 



Although the echinostome eggs are much alike in shape they differ 

 considerably in size. Even in the same species there is considerable 

 variation. Perhaps the largest echinostome egg of unquestionable 

 record is that of Pegosomum saginatum (Ratz), the length of which is 

 0.130 mm. and the width 0.089 mm., but even here there is great 

 variation in size. One of the smallest echinostome eggs is produced 

 by Monilifer spinulosus (Rud.), measuring but 0.069 to 0.072 mm. in 

 length by 0.048 to 0.050 mm. in width. Although variation in size of 

 eggs is common to nearly all digenetic trematodes, yet no species seems 

 to have greater variation than the records given for Echinostoma 







