10 ENTOZOA FOUND IN MAN. 



some time continuously with each other, and with 

 the head or scolex, they become detached, and live 

 separately for a certain period. In several known 

 species of cestoid worms, the separation from the 

 scolex is ejffected before the rings have arrived at 

 maturity ; each ring lives, moves about, is nourished, 

 and increases in size in this free state, and its repro- 

 ductive organs complete their development in the 

 same condition. This detached ring, which possesses 

 all the characteristics of animal life, is the adult 

 cestoid worm, which reproduces its species by means 

 of ova. 



Before the ovum has been expelled from the 

 several organs, there is developed in it an embryo 

 which neither resembles the proglottis from which it 

 proceeds, nor the scolex which has produced the pro- 

 glottis. It is, in fact, destitute of suckers, and armed 

 with six hooks which differ from those of the scolex 

 both in number and in form. 



Here, then, are three successive and distinct 

 individuahties, of which one forms the perfect animal. 

 How is the interrupted series between the embryo 

 and the scolex completed 1 Does the latter come 

 from the former by metamorphosis, or by gemmation 1 

 Before proceedmg further, the phases of alternate 

 generation in these successive individuals may be 

 recapitulated ; a ring is produced from the head by 

 gemmation ; and a six-hooked embryo is sexually 

 produced from the ring. The head is consequently a 

 nurse, accorduig to the nomenclature of Steenstrup, 

 and a scolex, according to that of Van Beneden ; the 

 ring, or proglottis, is the adult individual. 



No observer has traced in a decisive manner the 



