6 Laacllc B. Sturdevant 



DESCRIPTION OF AN UNUSUAL SPECIMEN OF'//. dimUluta 



This specimen was taken from the small intestine of a full- 

 grown brown or Norway rat {Mus dccnmanus Pallas). 



The length of Hymcnolcpis diminuta is given as from lo to 60 

 cm., but this specimen measures 99 cm., and.jf the length of the 

 loose portion of ripe proglottides found in the large intestines and 

 coming from this worm be added, the total length reaches one 

 meter. This is certainly phenomenal, as the next longest worm 

 in my collection coming from specimens of the rat is but 40.2 cm. 

 long. . This longest specimen was attached to the wall of the small 

 intestine within less than a centimeter of the pylorus and extended 

 throughout the length of the small intestine to within i dm. of the 

 opening into the large intestine. It was thus in life about equal 

 to the length of the small intestine of the full-grown rat in which 

 it was found, and that is about 1.5 m. in length. In the fixing 

 fluid it contracted to about two-thirds of its original length, 

 though even then the proglottides remained longer than is usual 

 in this species. 



The width of this specimen at 20 cm. from the head is 1.8 mm. 

 and gradually increases to 2.8 mm. at 40 cm. At 60 cm. it is 3.1 

 mm., at about 80 cm. it reaches its maximum width, 3.3 mm., 

 gradually decreasing from here to the end, wdiere the width 

 measures 2.5 mm. The maximum width is given as 4 mm., the 

 figure given by Packard (7 mm.) for his specimen from the hu- 

 man subject being regarded as doubtful. The scolex is subject 

 to great variation in regard to size and shape. Some of the more 

 usual shapes it assumes in the fixing fiuid are shown in figures 

 I, 2, II, and 12, the last showing the form of the scolex of the long- 

 specimen. In life the head is constantly changing in form as the 

 musculature of that region acts. The suckers or rostellum or 

 both may be extended or retracted in a great variety of ways, as 

 well as the scolex as a whole. In general the scolex is more or 

 less truncated or globular but flattened somewhat dorsoventrallv. 

 The width of the head is given as 200 to 600 jx ; in the specimen 

 under consideration it is 190 ix between the suckers with a dorso- 

 ventral measurement of 151 ix. The four suckers, spherical iu 



140 



