THE SCOLEX-STATE. 35 



in cod-fish, gurnards, congers, and even in cuttlefishes. From 

 the encysted condition in which the parasites are found in these 

 animals, it is easy to see that they have only made them their 

 temporary abode. That they are by no means at home in these 

 intermediate hosts seems evinced by their lively and restless 

 proceedings ; their four protractile feelers, with their countless 

 hooks, being employed most cleverly, to bore through the flesh, 

 the walls of the stomach, and the tunics of the various organs. 



The head end of the young Cestoidea takes, at a very early 

 period, the form of that of their sexually matured parents, whence 

 it is easy to distinguish to which species of cestoid worm they 

 belong. According to Van Beneden's suggestion, helminthologists 

 have designated such undeveloped sexless Cestoidea whose heads 

 have already assumed the parental form, as " scolices." From 

 their physiological signification these cestoid scolices have been 

 compared with the larvae of insects ; the comparison, however, is 

 not tenable, since every insect larva leaves the egg in its larva- 

 form, and is gradually changed into an individual insect capable 

 of propagation, whilst the scolices of the Cestoidea do not come 

 forth from the egg in the condition of scolices, nor are converted 

 into a reproductive tape-worm individual, but by sexless genera- 

 tion give birth to a great number of sexual individuals. Here, 

 therefore, we have to do, not with metamorphosis, but with an 

 alternation .of generations in which the scolex-forms play the 

 part of agamozooids. 



In studying the history of the Cestoidea, it must be strictly 

 borne in mind that all scolices, whatever be their form, are only 

 different stages of cestoid worms ; and, on the other hand, that 

 the cestoid embryos leave the egg in a form widely different from 

 a scolex. The embryos of the genera TcPMia and Bothriocephalus 

 are precisely similar, widely different as are the forms of the 

 so-called " heads " of these worms subsequently. The whole or- 

 ganization of these embryos seems specially adapted for the purpose 

 of digging and boring, a circumstance most favorable to them in 

 their wanderings. They possess, in fact, a very small rounded 

 body, (fig. 18 a), at one end of which six little hooks or claws 

 project, two in the middle and two on each side. Each pair of 

 these hooks is differently shaped from the others (fig. 18 b, c, d) } 

 and they are so arranged, that one of each form is placed on each 

 side of the embryo, so that the two innermost, the two middle, 



