THE CYSTIC ENTOZOA. 501 



human os uteri into the vagina. This organ, in its relations 

 and structure, appears to be the analogue of the cavity 

 described by Professor Owen, as opening into the posterior 

 orifice of Distoma clavatum, and supposed by him to be a 

 respiratory organ. 



A pyriform sac, communicating with the exterior by the 

 pore in front of the acetabulum, and two large, with occa- 

 sionally two smaller globular masses, would appear to be the 

 analogues of the reproductive organs. The pyriform sac 

 always contains highly refractive oil-like globules, but larger 

 than those in the chyle-receptacle. The two larger globular 

 masses are very constant, and, as well as the two smaller, 

 contain a mass of particles apparently nucleated. From the 

 two larger, I have only been able to see faint traces of what 

 appeared to be ducts passing in the direction of the smaller 

 masses, and towards the neck of the pyriform sac. Whether 

 these convoluted bodies be ovaries or convoluted oviducts, 

 and the pyriform sac a uterus ; or whether the former be 

 the testes, and the latter the female organ, as in the arrange- 

 ment described in the other Distomas ; or whether they be 

 reproductive organs at all, I have failed in satisfying myself, 

 in consequence of the delicacy of their texture, and the com- 

 paratively dense integument of this part of the animal. 



This Distoma possesses a vascular system forming a net- 

 work throughout the body. The two principal trunks, as in 

 the other genera, passing along the sides of the body and 

 being most apparent at its posterior third. 



I. ACEPHALOCYSTIS. 



Completely buried in the textures of the infested animal 

 young only consisting of three membranes; adult of four, the 

 external one belonging originally to the infested being. 

 Nourished by epithelial cells, which are contained in one of the 



