THE CCELOMATA INVERTEBRATA 195 



The body has the form of a long narrow ribbon, well deserving its 

 name of " tape " worm, and may reach a length of many feet or 

 yards ; one is recorded as attaining the enormous length of thirty 

 metres. At the front end is a tiny knob-like swelling, the head, by 

 which the animal attaches itself to the wall of the alimentary canal, 

 and this is followed by a very thin thread-like unsegmented portion, 

 the neck, and the head and neck together constitute the scolex. This 

 part is usually missing in laboratory specimens, and is so small that 

 it would be readily overlooked. At the posterior end of the neck 

 are indistinct transverse grooves, which become more and more 

 distinct as we pass backwards, soon dividing the body up into a series 

 of discrete segments or better proglottides, which constitute the 

 genital part of the animal, the strobilla. The proglottids have the 

 form of narrow transversely placed rectangles, but farther back they 

 are longer, forming almost square sections and then longitudinally 

 running rectangles. The main part of the body is then composed 

 of a series of segments, and so presents a superficial resemblance to 

 a segmented Annelid, but they are not truly typical metameres or 

 somites. Each contains little more than a complete set of repro- 

 ductive organs, which are immature at the front end. When fully 

 formed the proglottids are termed mature, and at the hinder end, 

 where they are almost filled up with a much branched uterus laden 

 with eggs, they are said to be ripe. In this condition they are fated 

 to drop off from the end of the chain either singly or in groups, and 

 passing to the outside with the faeces of the host bring about the 

 dissemination of the species. So it comes about that the ripe pro- 

 glottids are shed from the end of the series, new ones are formed just 

 behind the neck, which is therefore the growing point, and the host 

 is not free of the pest, however many proglottids are removed, as 

 long as the scolex remains behind, and this is always difficult to 

 dislodge. 



The head is the organ of attachment, and for this end is furnished 

 with clinging organs in the form of suckers and hooks. The suckers 

 in T. solium are oval, cup-shaped, strongly muscular structures situ- 

 ated on the head, to which they give a rough rectangular shape. In 

 front of the suckers is a broad conical projection, the rostellum, 

 furnished with a double row of strong chitinous spines. This is 

 capable of being protruded and retracted. The number and shape 

 of the suckers and presence or absence of a rostellum or its spines 

 form important characters, by means of which the various species 

 of tapeworm may be distinguished. 



Living as it does in the alimentary canal, it is surrounded by food 

 in a diff usable condition, and as a result we find it devoid of a mouth, 

 a gut, or any form of digestive system, feeding taking place by 



