DISTOMDM CIRRIGERUM. 301 



(6) Section of sporocyst after budding is completed. Tlie bkstomercs 



have divided into small cells possessing nuclei, which stain with 

 great dilScully. No yolk-cells are now visible. 



(7) A sporocyst in surface view, dividing by fission into two. 



(S) Sporocyst in section; it becomes bcan-sliaped,and a delicate irregular 

 cuticle is produced. The fundament of the male copulatory organs 

 may appear. Often, however, it is not formed until later. 



(9) The irregular cuticle becomes thicker. 



(10) Cercaria-cyst is formed, and embryo is seen in longitudinal section. 



The cyst may be produced at some little depth within the embryo, 

 and hence some of the cells of the embryo become excluded from 

 the future development (c.v. c). The fundament of the male 

 copulatory organs has increased. Perhaps cystogen cells occur 

 (<7- c.). 



(11) Cortex is formed, gut appears, also suckers and gonads. 



(12) The embryo in longitudinal section, showing the final stages of 



development. The inner sheet of cortex has become split to 



form the ventral surface; cuticle with spinelets is produced by 



the cortex. 



Fig. XII. — X 280. The sexual form escaping from the cercaria-cyst. It 



is viewed ventrally and as a transparent object. Notice the symmetrical 



arrangement of the spinelets, the genital atrium opening at first into the 



depression of the ventral sucker and the V-shaped excretory bladder. 



Fig. XIII. — X 400. Embryo in longitudinal section nearly ready to 

 emerge from cercaria cyst. Notice genital atrium, cirrus, uterus, and the 

 origin of the excretory bladder. 



Fig. XIV. — X 880. A small piece of the cortex with the underlying cells 

 of an embryo soon after the cercaria-cyst is formed. 



Fig. XV. — X 880. A small i)iece of a somewhat older embiyo; the under- 

 lying cells become differentiated into ''' epidermal cells," muscular cells, 

 branched and vesicular cells. The thin cuticle and spinelets are produced. 



Fig. XVI. — X 400. Transverse section of the adult. The cuticle is raised 

 into scales, but no spinelets were visible. The thin layer of protoplasm (pi.) 

 under the cuticle is the remainder of the embryonic cortex. A few circular 

 and longitudinal muscle-fibres are visible. 



Fig. XVII. — X 400. Longitudinal section to show curious inflated struc- 

 tures, which are probably an artificial production. 



Fig. XVIII. — X 400. Transverse section of the anterior portion of a de- 

 veloping embryo to show the origin of the gut.ca;ca, pharynx, and nervous 

 system. 



