ENTOZOA. 75 



segments are laden with ova. They adhere by the fore part of the 

 head to the mucous surfaces of the appendices pyloric^e, and cast off 

 the ovigerous segments, sometimes in their whole length ; so that 

 headless tapeworms are found in the lower part of the intestine, 

 whilst a number of heads without bodies may be observed adhering 

 to the pyloric appendages between other tapeworms of very diflferent 

 lengths. The heads thus left behind generate a new series of perfect 

 joints in the following way: the joint next the head is divided by a 

 transverse fissure into two, each of which repeats the same process 

 as soon as it is somewhat grown. Whilst the joints multiply in this 

 way, they continue to increase in size, and so become removed from 

 the head ; but at a certain distance from the head, this mode of sub- 

 dividing ceases, and the whole nutritive power is applied to the de- 

 velopment of the organs of generation. During winter the Bothrio- 

 cephalus piinctatuSy still adhering firmly to the mucous surface of the 

 pyloric appendages, grows to its full length, the segments with 

 the generative organs being formed ; but no ova can be seen. 

 These begin to appear at the commencement of spring in the 

 posterior joints, and by degrees fill the uteri of all the joints, until 

 they occupy those which are close to the head, when the separation 

 from the head before described ensues, and this last-named member 

 is left to repeat the important process. No single joint of a tape- 

 worm can develope a head, and so form a new nutrient individual ; 

 the transverse fission relates only to the dissemination of the fertile 

 ova. But the joints, so separated, may be regarded as "generative 

 individuals," and those of the Tcenia solium live and move about, 

 and closely resemble Distomata, They may be seen in all grades 

 of development, some as infants, others adolescent, and the terminal 

 ones fully formed and pregnant. 



The eggs of some Cestoidea have a single shell or tunic, which 

 is colourless in Tcenia literata, T. Scolecina^ as well as in the genera 

 CaryophyllcEUS and Tricenoplioriis ; but is of a brown colour in 

 many species of Bothriocephalus. The round eggs of Tcenia 

 amphitricha, T. serrata, and T. bifaria, and the elliptic eggs of T. an- 

 gulata and T. villosa, have two colourless tunics. In Bothriocephalus 

 proboscideus and Tcenia porosa, the eggs have three colourless 

 tunics. In Tcenia solium, the innermost of the three tunics is thick 

 and becomes a yellowish brown in the ripe eggs. In Tcenia in- 

 fundibuliformis and T. planiceps, the outer tunic has two long 

 pointed processes on each side : in T. cyathiformis it is provided 

 with two round vesicular appendages. In Tcenia injiata, the inner- 

 most of the three tunics is transversely elliptical, the middle tunic is 

 produced into two long diverticula, and the outer tunic has two long 



