WORMiS. 185 



Branch V. — VERMES. 



The great ami varR'(l assemblage of animals which are jmt tooether umler tlie 

 eomraon ilesignatitui of woi'ms does not jjvesent a homogeneous group for study. On 

 the contrary many distinct tyjies have been thrown together to make the branch of 

 Avorms. Indeed it has been a long-standing current joke among zoologists that this 

 [lart of tlie zoological system was the garret, or as the German has it the Kilmpelkani- 

 uuM-, into which everything was carelessly thrown that did not properly belong else- 

 where, and had been therefore rejected from the other portions of the system of classi- 

 tiiation. The worms have thus come to be a collection of forms whose outside affini- 

 ties extend to nearly all other animals, while among themselves they fall into classes 

 not closely related with one another. These classes shade off in some cases towards 

 other branches ; thus the rotifers approach in their organization the molluscan type, 

 wliile the Annelida proper show in some respects unmistakable similarity with the 

 insects. Other classes, like the Acanthocephali and Enterojmeusti {Hahuioglossus) 

 attain an anatomical configuration which gives them a certain indejiendcnce, a ])lace 

 ajiart, in the zoological system. In brief, as the limits of the branch of wt)rnis are 

 vague, and its components multifarious, therefore it is difficult to dctlHe the worms 

 with an accuracy corresponding to the requirements of .-i rignrous science. Tlie fol- 

 lowing definition is the most satisfactory I am able to gi\(' : — 



A worm is a bilaterally symmetrical .animal, with a distinct head characterized by 

 the presence of the princip.al nervous centre or so-called brain. It is distinguished 

 fi'om molluscs by the absence of a shell and of that nioditication of the skin, named 

 the shell gland, which forms the shell and is jiresent at least in a rudimentary condi- 

 tinn in all true molluscs. It is distinguished from Crustacea and insects by the want 

 of jointed limbs, and finally from the tunicates and vertebrates by the lack of a struc- 

 tural a.xis, the so-called notochord or chorda dorsalis, which gives the name of Chor- 

 data to the divisions last mentioned. As far as at i]resent known no worm has a true 

 liver, a calcified internal .skeleton, an organ homologous with the endostyle of ascidians 

 and thyroid gland of vertebrates, any tracheal tubes like those jierforming respiration 

 in insects, or finally any unicellular hairs. In fact a worm must be recognized as such 

 rather by the ])rocess of exclusion than by the observation of jiositive characteristics. 



To the scientific zoologist the worms are most interesting subjects of study, not 

 only from their manifold variety and strange life histories, but also from their relation- 

 ship with the higher types, the ancestral forms of which .are with good reason sup- 

 posed to be more nearly represented by certain wciinis tliaii by any other anim.als now 

 existent. The mind links in imagination these nbscurc and humble creatures with the 

 most exalted org.anisms, and finds in tlu' scci-ct'^ uf their low organization the key to 

 the complex structure of the highei- animals. Wc, however, shall not enter ujion 

 these difficult discussitms, where debate is still active, .and the final decision uncertain. 

 Instead we shall be sufficiently occupied with studying the jirincipal and most in- 

 teresting forms of vermian life as to their appearances and habits. Although a worm 

 is by popular fancy a loathsoine thing, yet only some of them deserve opprobrium, 

 while many others are objects of great beauty, .and others again are quaint ; a few are 

 of great utility to man, and yet others are among man's most dreaded enemies. 



