THE CESTOIDEA 



there is developed from the superficial blastomeres of the embryo a 

 ciliated mantle or " embryophore " enclosing the solid six-hooked 

 embryo, which is developed from the central mass of blastomeres. 



FIG. XI. Development of Bothriocephalus latiis, L. (after Schauinsland). 



1. Segmentation is completed ; some cells of the blastosphere have migrated through the 

 yolk, and have flattened out to form (c) a " yolk envelope." A second set of superficial cells of 

 the embryo have grown over the remainder, and have formed a layer (e) of flattened cells, the 

 embryophore (Schauinsland's " ectoblast "). The remainder (rf) of the blastosphere will 

 develop into the six-hooked embryo. 



2. A later stage in which the embryophore (e) is becoming thicker. 



3. The larva has been artificially pressed out of the shell, the operculum (s') being 

 pushed off. The embryophore has developed cilia. The yolk envelope remains in the egg 

 shell, and now the yolk (y) is seen to consist of separate cells. 



4. A free-swimming larva. The embryophore (e) is much swollen by the water. The six 

 hooks are developed. 



This embryo leaves the thick operculated shell, still enclosed in the 

 embryophore in B. latus, though in other species it is not ciliated and 

 is left behind ; by means of it the onchosphere is enabled to swim 

 freely in the water for at least a week, rotating about an axis that 



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