54 



ESSENTIALS OF ZOOLOGY 



parenchyma of the worm. Enzymotic processes are only 

 necessary in building up the food to suit the constitution of 

 the cells of the worm, and it is probable that the specificity 

 usually marked with regard to hosts is connected with the 

 peculiarities of the worm metabolically. 



Nerve cord 

 Excretory vessel 



Yolk gland 



Circular muscle layer 



Ectoderm 



Testis 

 Uterus 



Mesenchyme with 

 longitudinal muscles 

 and lime cells 



FIG. 24. Transverse section of another common tapeworm of the dog, Dipy- 

 lidium caninum. Note In this form the reproductive organs are paired. 



The proglot tides are concerned in forming the generative 

 organs. The latter are initiated just behind the neck and 

 pass through phases of development in the successive segments, 

 culminating in the terminal segments, which are full of eggs. 

 The proglottides are being constantly renewed in the neck, 

 and the ripe segments are cast off from the posterior end. 



