TITANOSOMA AND POLYMICRODON IN ENGLAND 145 



shape of the abdominal segments. The Metopidiotrichidae 

 differ in various characters of the head of the male, in the 

 possession of thirty-two abdominal segments and of only one 

 pair of coxal sacs. Though their posterior gonopods are 

 three-jointed, they are extremely unlike those of Brachy- 

 chaeteuma ; their anterior gonopods are at present unknown, 

 though this much is certain, that they can have no close 

 resemblance to those of our genus. That the Chordeumidee 

 present fundamental differences, not only in facies but also in 

 the structure of all their reproductive organs, is too obvious to 

 need further emphasis. 



The genera of the Conotylidae are all more or less unsatis- 

 factorily described ; it is plain however that they have no near 

 relationship with Brachychaeteuma. Their anterior gonopods 

 are yet for the most part quite unknown. A general re- 

 semblance exists between Brachychaeteuma and the Mastigo- 

 phorophyllidas, and there is a further agreement between 

 them in the absence of sucker-discs. In the male reproductive 

 organs, on the other hand, we find extensive differences, which 

 are not confined to the pseudoflagella. The syncoxite of the 

 anterior gonopods shows in Brachychaeteuma a strong central 

 compression, and exceeds in size the telopodites, which are 

 pressed together in the middle. In the Mastigophorophyllidae 

 both the coxites and telopodites remain separated in the 

 middle line, and the latter are so strongly developed that the 

 former only constitute a narrow base for them. Scarcely less 

 important are the differences in the posterior gonopods. 

 Correspondingly, Brachychaeteuma exhibits structures for the 

 conveyance of the sperm which are widely different from 

 those of the Mastigophorophyllidae. To the Orobainosomidas, 

 Brachychaeteuma shows similarity not only in the form of the 

 abdominal segments, but also in regard to the posterior 

 gonopods. Again, however, there are conspicuous differences : 

 gonopods and sternite entirely different; and telopodites 

 adapted indeed to receiving the sperm, but with sacs which 

 open towards the syncoxite, without any fine canal. Further- 

 more, in contrast with the present genus, the Orobainosomidae 



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