Glass 3. Gestoda. 151 



after its shell is dissolved by the digestive fluids^* bores through 

 the wall of the gut and becomes a proscolex. 



As regards their structure the Tapeworms are, excepting for the 

 absence of the alimentary canal, closely connected with the Trema- 

 todes. The genitalia are hermaphrodite, of a very complicated 

 nature ; in each segment, there is a separate genital apparatus, which 

 has no connection with those of the otber segments. The genital 

 aperture is either on the ventral side of the segment, or on its margin. 

 The parasitic genera, Amphilina (in the Stm-geon), and Garyophyllxus (in the 

 Oarp), seem to be a transition towards the Trematodes, for they do not form 

 chains. The unsegmented hody contains but one reproductive apparatus i 

 like the rest of the Cestoda, they have no gut, and agree also with them in 

 certain special arrangements of the genitalia. Some other Tapeworms are like 

 the above-mentioned forms, in so far as they appear to be entirely unsegmented, 

 although they exhibit essentially different arrangements, for an inner segmentation 

 is clearly manifest in the multiplicity of the reproductive organs. Among 

 such forms, a separation of the reproductive individuals does not occur, and a 

 chain of this kind may be compared with a Ooral-colony, some of whose 

 polyps are in closer connection than usual. As an example of Cestodes 

 showing this external continuity, but internal metamerism, the Strap-worm, 

 lAgula simpUaissima, parasitic in the digestive tract of different Water-birds (in 

 Fish in the cystic stage), may be mentioned. 



Most of the Tapeworms of Mammalia and Aves belong to the 

 genera. Taenia and Sothrioeephalus, chiefly to the former. Numbers 

 of other genera are known particularly in Pisces. 



1. Tssnia. The head is furnished with a circle of four suckers. Upon the 

 middle of the anterior end there is, in many species, a crown of recurved hooks, 

 which may be numerous, and situated upon an elevation (rostellum) ; in others, 

 however, the hooks may be entirely wanting. The ripe proglottis may be 

 elongate or short and wide ; it contains a branched uterus. The genital aperture 

 is usually at the edge of the segment. 



(a) T. solium lives in the alimentary canal of Man. The scolex with a crown 

 of hooks, the ripe proglottides considerably longer than broad ; the former about 

 as large as a pin's-head, the latter 5 m/m broad. The chaiu attains a length 

 of about 3, to 3J m. The ripe proglottides, and the thick-shelled eggs, con- 

 taining embryos pass out with the excreta. If they be eaten by a Pig, the 

 egg-sheU dissolves, and the six-hooked larva bores through the gut into the body, 

 where it usually takes up its abode in the muscles, more rarely in the heai-t 

 or brain; there it grows considerably, and turns into a bladder- worm or 

 proscolex (Cysticercus cellulosse), a cestode head of the same appearance as that 

 of the adult Tapeworm, but with an appendage behind in the form of a vesicle 

 the size of a pea, filled with fluid, ui which the head is invaginated. When it is 

 taken into the digestive tract of Man, the bladder atrophies and the head develops 

 into the Oestode-chain. More rarely the proscolices' are found iu various other 

 Mammals. They sometimes occur in Man in places where they may prove fatal, 

 in the brain, eye, or wall of the heart. Man, like the Pig, may occasionally 

 take in eggs containing embryos through the mouth. 



(6) T.mediocanellata{=T.saginata, Lbtjck.), also found in the digestive iract 

 of Man; in most countries more common than T. solium. The head without 



* This shell is not an egg-shell in the usual acceptation of the term, but a 

 membrane secreted by the embryo. The ' ' eggs " are, in reality, encysted embryos. 



