164 UNSEGMENTED "WORMS." 



hematuria, etc. The sexes are separate, and the male 

 (about half an inch in length) carries the more thread-like 

 female (about an inch in length) inserted in a groove or 

 gynsecophoric canal. Man is probably infected from bad 

 water, but the history of the parasite is still uncertain. 

 The embryos are passed out in the urine. 

 Monostomum, with one sucker, adults in ducks, young in 

 Planorbis. 

 The relationships of the class are on the one hand with the free-living 

 Turbellarians, on the other hand with the parasitic Cestodes. 



A few interesting simple forms like Temnocephala found in Crustacea 

 and Vertebrates, seem not to be truly parasitic, for they live on minute 

 organisms and only receive shelter from the host. In the ciliation of 

 the ectoderm and in some other respects these forms closely resemble 

 Turbellaria. 



Class Cestoda. Tape-worms. 



The Cestodes are internal parasites, whose life history 

 includes a bladder-worm (proscolex) and a tape-worm (strobila) 

 stage, the former in a Vertebrate or Invertebrate host, the 

 latter (with one exception) iii a Vertebrate. In a few cases 

 the body is unsegmented, e.g. Archigetes and Caryophyllseus, 

 with one set of gonads ; in a few others, e.g. Ligula, there 

 is a serial repetition of gonads without distinct segmentation 

 of the body ; in most cases, e.g. Taenia and Bothriocephalus, 

 the body of the tape-worm forms a chain of numerous joints or 

 proglottides, each with a set of gonads. Thus the class in- 

 cludes tra?isitions from unsegmented to segmented forms, but 

 the latter are imperfectly integrated. The general form of 

 the body is tape-like and bilaterally symmetrical, with hooks, 

 grooves, or suckers ensuring attachment to the gut of the host. 

 The body -wall consists of a cuticle and a well- innervated 

 epidermis, within which there is parenchymatous connective 

 tissue, often with cortical deposits of lime, and at least two sets 

 {longitudinal and transverse) of unstriped muscles. The 

 nervous system consists of two or more longitudinal nerve- 

 strands and anterior ganglionated commissures ; there are no 

 special sense organs. There is no alimentary system; the 

 parasite floating in the digested food of its host absorbs soluble 

 material by its general surface. There is no vascular nor 

 respiratory system, and a body cavity is represented merely by 

 irregular spaces in the solid parenchymatous tissue. In some 

 of these spaces there are " flame cells," which lie at the ends of 



