POSSIBILITY OF DIRECT DEVELOPMENT. 671 



through the hands, which touch and stroke this animal. Thus in 

 both cases the transmission takes place indirectly, and this explains 

 why the tape-worm occurs in man only in small numbers, or even 

 singly. In all cases the hosts have in some way or other come into 

 close contact with the dog. Nor does it surprise us to learn that 

 these hosts are most frequently children, since they generally treat 

 dogs with the most unrestrained familiarity. 



Hering, however, cannot reconcile himself to the significance 

 which the change of hosts possesses in the life-history and circulation 

 of the parasites, and is, moreover, of the opinion that the Cysticercoid 

 state is by no means necessary to the development of Tcenia cucumerina 

 (nor, indeed, to any of the other tape-worms), and that the worm may 

 be developed in the subsequent host, directly from the six-hooked 

 embryo. To test the accuracy of this supposition, he fed fourteen 

 dogs with the ripe terminal joints of T. cucumerina,^ and afterwards 

 found the tape- worm in twelve ; but the various results agree so little 

 with the stages of the experiment, and otherwise contradict each other 

 so much, that the only thing that can be concluded from them is the 

 great frequency of the parasite, and especially in young dogs, such as 

 Hering used (Krabbe found T. cucumerina in 87 out of 185 cases in 

 Copenhagen, or nearly half of the dogs which he examined in search 

 of Helminths). But even if these feeding experiments are not con- 

 clusive, they are by no means without interest, since they show that 

 the transformation of the Cysticercoid into the adult tape-worm only 

 occupies a short time. For example, a dog only thirty-one days old 

 was found to contain a T. cucumerina 15 inches long, and with 

 perfectly ripe proglottides. Another dog ten days old contained a 

 tape- worm 10 lines in length, with distinctly defined and already 

 oval joints. The supposition that the dog is infected more easily by 

 sucking its mother than by licking seems hardly probable from these 

 cases, for then the date of the infection must coincide with the first 

 day of life. We can therefore hardly be wrong in supposing that for 

 its development from the Cysticercoid to the ripe proglottides, T. 

 cucumerina requires about two to two and a half weeks. 



In conclusion, a few remarks on the structure of the sexual organs 

 may be added. It has already been mentioned in regard to these 

 tape-worms that the genital pore, or rather the outlet of the sexual 

 organs (since the male and female ducts open near each other without 

 any special sexual cloaca) is double. One part lies on the right, and 

 the other on the left lateral margin, both being about the middle, or 

 but little behind it, as, indeed, may be observed with the naked eye, 



* " Beitrage zur Entwickelungsgesch. der Eingeweidewurmer," Wilrteml. naturwiss. 

 Jahreshcfie, p. S56, 187 S. ^. ... , . ... „^ 



Digitized by Microsoft® 



