204 TAPEWORMS OF HAKES AND RABBITS STILES. 



well defined, as in Anoplocephala mamillana, A. wimerosa, Cittotccnia 

 marmotce, C. pectinata ; or they may be less distinct (C. variabilis, C. 

 prcecoquis)-, or they may be totally absent (C. variabilis), in which case 

 the uterine tube appears as an enlarged sac. In some species where 

 they are at first well developed (Anoplocephala mamillana and A. 

 wimerosa) their boundaries may disappear in the older segments, the 

 uterus appearing as a sac. 



The uterus of C. denticulata seems to be more complex and requires 

 further study. 



II. The genus Thysanosoma presents a totally different uterus. The 

 anlage is originally a simple transverse tube as in the cases just men- 

 tioned, but the increase in size takes place by two different methods, 

 which gives rise to quite a complicated structure. First, the anlage 

 increases greatly in length, giving rise to numerous folds running longi- 

 tudinally with the worm; next, this undulate tube forms blind pouches 

 which are surrounded by a heavy layer of connective tissue, giving the 

 pouch a characteristic appearance; the ova are deposited in these 

 pouches and the original tube remains empty. The uterus of Stilesia 

 globipunctata bears a certain resemblance to the uterus of Thysanosoma 

 in that the egg pouches have a somewhat similar structure. 



III. A third type of uterus appears to be presented by the genera. 

 Andrya and Moniezia, and this type will require considerable study 

 before it can be correctly interpreted. From the present status of our 

 knowledge, however, it may be described as a complex system of 

 branching and anastomosing tubes, a single set being present in 

 Andrya, a double set in Moniezia. In the later stages of the uterus 

 the boundaries of the tubes disappear and the uterus appears as a sac. 



A transverse uterine anlage has not yet been recorded for these 

 genera, except in the case of Moniezia trigonophora^ for which species 

 Stiles and Hassall 1 in 1893 have figured a short transverse canal which 

 represented the earliest uterine stage they observed. 



An interesting problem now presents itself, namely: In what relation 

 do these types stand to each other? Have we here three parallel 

 series of originally single-pored cestodes, each series with a particular 

 type of uterus, and have the double pores been acquired independently 

 after the three types of uteri became established? Or, do the single- 

 pored forms represent one branch and the double-pored forms represent 

 another, and have the three different types of uteri been developed 

 independently in each branch? 



The former supposition appears to me much the more probable, for 

 in Thysanosoma giardi and Cittotcenia variabilis we find both single and 

 double pored segments. 



This case represents one of the most interesting cases of homo- 

 plasy which has ever been observed in helminthology and should be 



1 Revision of adult cestodes of cattle, sheep, and allied animals, Bull. 4, Bur. An. 

 Ind., U. S. Dept. Agric., pis. vm, fig. 5 ; ix, fig. 3. 



