74 PLATYHELMINTHES 



living animals. They have no alimentary canal, probably 

 no organs of special sense, and, except in the head, the ner- 

 vous system is feebly developed. On the other hand, the 

 organs needed for the reproduction of the species are enor- 

 mously developed, so that in the more mature portions of 

 the animal, the ovaries, testes, and accessory organs occupy 

 nearly the whole space. Can you explain this condition? 



CROSSOBOTHRTUM LACINIATUM 



This tapeworm passes its adult life in the intestine (spiral 

 valve) of the sand shark. Cestode larvae which may be the 

 young of this species are abundant in the cystic duct of the 

 squeteague. How the developing eggs and embryos are con- 

 veyed from the shark to the squeteague is not known. The 

 transfer of the larvae from the squeteague to the alimentary 

 canal of the shark can be easily understood. 



Adult Stage. — 1. Notice specimens that are attached to 

 the wall of the intestine of the shark. 



2. Observe movements of specimens in a dish of sea water. 

 Do the suckers have independent movements? 



3. With a low power of the compound microscope, or with 

 a hand lens, note that the worm is made up of a head por- 

 tion, the scolex, and of numerous "segments," the proglottids. 

 What is the relative size of the proglottids in the different 

 regions of any specimen? Where are new proglottids pro- 

 duced? (See Curtis.) Are the proglottids attached to one 

 another with equal firmness in all parts of the body? Note 

 their peculiar shape, and how they are connected together. 

 In the above examination, if living material is used it will 

 often be desirable to stretch portions of the animal very 

 gently with your forceps. 



4. Note the number and arrangement of the disk-like 

 suckers. How are they borne on the scolex? Do you find 

 each sucker to be entirely simple? 



Draw the adult worm. 



5. Cut from the head end of a living specimen a piece 



