12 GUIDE TO THE STUDY 



to open through a dorsal pore near the center of the anterior 

 testis. Its significance and function are matters of much 

 dispute. 



The Mehlis gland, formerly regarded as a shell gland, surrounds 

 the junction of the oviduct and the yolk reservoir. It is in 

 reality an aggregation of unicellular glands. 



The uterus is a much convoluted tube packed with eggs, 

 occupying the whole median portion of the body between the ovary 

 and the ventral sucker, within the rami of the intestine. It 

 opens through the genital pore. 



The egg is dark brown, ovoid, and, like most fluke eggs, 

 possesses a cap, or operculum, through which the embryo escapes. 

 Is the opposite pole evenly rounded? 



Excretory System.— Running forward from the excretory pore 

 is the main duct of the excretory system, appearing as a clear 

 median tube which extends forward to the region of the seminal 

 receptacle where it bifurcates and is continued forward as a 

 slender tube on either side to the anterior region of the worm. 

 The finer tubules and their ultimate endings as the so-called 

 flame cells cannot be seen in these preparations. 



Nervous System. — The paired cerebral ganglia can be seen as 

 somewhat stellate, more deeply stained spots laterad and dorsal 

 to the middle portion of the oesophagus. Indications of the 

 origin of the anterior and posterior nerves can be seen in favorable 

 specimens. 



The circulatory and respiratory systems are not present in the 

 Trematoda. 



OTHER SPECIES 



Frog lung flukes belonging to the genus Pneumonaeces are 

 readily available and should be compared with Clonorchis. In 

 the lack of the latter they may even be used as a type. Note 

 particularly the feeble development of the ventral sucker, the 

 shape of the testes and ovary, the distribution of the vitellaria, 

 and the extent of the uterus. 



The Liver Fluke of the Sheep. — This species, Fasciola hepatica, 

 which is so widely used as a type in courses in general zoology, 

 should now be examined in the light of the above studies. Note 

 the very great development of the branches, or caeca, of the 

 alimentary canal, the extensively branched testes, the smaller 

 ovary and restricted uterus, and the position of the genital pore. 



