ANNULOIDA : SCOLECIDA. 185 



ganglia, which se^hd filaments backwards ; but there is con- 

 siderable obscurity on this point, and it has been asserted 

 that the nervous system is entirely wanting, or that there is 

 only a single ganglion. The " water-vascular system " con- 

 sists of a series of long vessels which run down each side of 

 the body, communicating with one another at each articula- 

 tion by means of a transverse vessel, and opening in the last 

 joint into a contractile vesicle. It thus appears that all the 

 joints are organically connected together. Whilst the "head 5 ' 

 constitutes the real animal, it, nevertheless, contains no repro- 

 ductive organs, and these are developed in the joints or 

 segments (fig. 68, 4), which are produced from the head poste- 

 riorly by budding. After the first joint, each new segment is 

 intercalated between the head and the segment, or segments, 

 already formed ; so that the joints nearest the head are those 

 latest formed, and those furthest from the head are the most 

 mature. Each segment, when mature, contains both male 

 and female organs of generation, and is, therefore, sexually 

 perfect. To such a single segment the term " proglottis " is 

 applied, from its resemblance in shape to the tip of the tongue. 

 The ovary is a branched tube, which occupies the greater 

 part of the proglottis, and opens, along with the efferent duct 

 of the male organ, at a common papilla, which is perforated 

 by an aperture, termed the " generative pore." The position 

 of this pore varies, being placed in the centre of one of the 

 lateral margins of the proglottis in the common Tape-worm 

 (T(E?iia solium), but being situated upon the flat surface of the 

 segment in the rarer Bothrioccphalus latus. These two elements 

 namely, the minute head, with its hooklets and suckers, 

 and the aggregate of the joints, or proglottides together 

 compose what is commonly called a " Tape-worm," such as is 

 found in the alimentary canal of man, and of many animals. 

 The length of this composite organism varies from a few inches 

 to several yards. 



Singular as is the composition of the mature Tape-worm, 

 still more extraordinary are the phenomena observed in its 

 development, of which the following is a brief account : 



" Proglottides," or the sexually mature segments of a Tape- 

 worm, are only produced within the alimentary canal of man, 

 or of some other warm-blooded vertebrate. The development 

 of the ova which are contained in the proglottides, cannot, 

 however, be carried out in this situation ; hence the compara- 

 tive harmlessness of this parasite, and hence the name of 

 " solitary worm." which is sometimes applied to it. For the 

 production of an embryo, it is necessary that the ovum should 



