NEMERTEA. 



175 



Life Histories. 



ADULT, SEXUAL, OR TAPEWORM 

 STAGE. 



NON-SEXUAL, PROSCOLEX, OR BLADDER- 

 WORM STAGE. 



1. Tcenia so Hum, in man, with four 

 suckers and many hooks. 



2. Tcenia saginata or mediocanellata, 

 in man, with four suckers, but no hooks. 



3. Bothriocephalus latus, in man, with 

 two lateral suckers, but with no hooks, 

 with less distinct separation of the prog- 

 lottides than in Tcenia. 



4. Tcenia echinococcus, in dog. 



5. Tcenia ccenurus, in dog. 



6. Tcenia serrata, in dog. 



7. Tcenia cucumerina, in cat. 



8. Tcenia elliptica, in dog. 



1. Cysticercus celluloses, in muscles of 

 the pig. 



2. Bladderworm in cattle. 



3. The ciliated, free swimming embryo 

 becomes a parasite in the pike or burbot, 

 but without a distinct bladder-like stage. 



4. Echinococcus veterinorum, in domestic 

 animals, and sometimes in man, producing 

 brood capsules, which give rise to many 

 " heads." 



5. C ceriums cerebralis, causing sturdie 

 in sheep, producing numerous " heads." 



6. Cysticercus pisiformis, in rabbit. 



7. Cysticercus fasciolaris, in mouse. 



8. Cysticercus in dog louse or perhaps 

 in flea. 



The Cestodes are closely connected with Trematodes by such forms as 

 Amphilina, Caryophyllcvus, Archigetes. Zoologically, they are interest- 

 ing, on account of their life histories, the degeneration associated with 

 their parasitism, the prevalence of self-impregnation, and the complexity 

 of the reproductive organs. Practically, they are of importance as para- 

 sites of man and domestic animals. The medical student should consult 

 Leuckart's great work, The Parasites of Man, part of which has been 

 translated by W. E. Hoyle (Edin. 1886). 



Class NEMERTEA. Nemertines. 



The Nemertines are worm-like animals, unsegmented, and 

 generally elongate in form. Almost all are marine ; most, if 

 not all, are carnivorous. Among their characteristics, the 

 following are most noteworthy : The skin is ciliated ; there 

 is a remarkable retractile proboscis ; the head bears a pair of 

 ciliated pits ; the nervous system consists of a brain, a com- 

 missure around the proboscis^ and two lateral nerve cords ; 

 there is a ccelomic vascular system, a pair of anterior nephridia, 

 and a simple reproductive system. The sexes are usually 

 separate. In some the development includes a peculiar pelagic 

 larval stage ; in others there is no metamorphosis. 



External Appearance. 



Some are ribbon-like, others thread-like, and the cross 

 section is generally a flattened cylinder. They vary greatly 



