1920.] R . B . Seymour Se^wei.l : Mesocoelium sociale. 



83 



ripe ova, though in the smaller examples only a few were present, 

 whereas in the large ones the coils of the uterus were densely 

 crowded. 



Table II. 



Dimensions of Mesocoelium sociale (lyiihe) in millimeters. 



In the case of a living example the body when extended 

 showed a length of 2"65 mm. and a breadth of 0'30 mm., but when 

 fully contracted the length was only i'i8 mm. and the breadth 

 had increased to o"65 mm : in this example both suckers gave a 

 measurement of o'i8 mm. in the transverse diameter, but the oral 

 sucker was somewhat elongate in shape and had an antero- 

 posterior length of 0*235 tnm. 



The oral sucker occupies the rounded anterior end of the 

 body and, as is only natural, varies in size in specimens of -varying 

 degrees of growth, being smaller in specimens with a small body- 

 length and larger in those whose growth and development has 

 proceeded further. Its general outline is found to vary in 

 different individuals ; in some cases, as in Examples i, 3 and 4 in 

 Table II, its antero-posterior length is greater than the transverse 

 diameter, whereas in others, such as example 5, it is the transverse 

 measurement that is the greater. This difference is probably 

 directly correlated with the degree of extension or contraction of 

 the anterior end of the body, in the extended condition the long 

 diameter being antero-posterior, while in the contracted state it 

 becomes transverse. The mouth is subterminal in position 

 and it leads back into the cavity of the oral sucker : around its 

 margin in young immature specimens is a double ring of small 

 papillae, but as the worm grows these appear to become propor- 

 tionately smaller and in the largest examples seem to have 

 disappeared entirely. 



