/------------^-----------\ /--------------^--------------\ =Order= ZYGOBRANCHIATA, AZYGOBRANCHIATA, or Streptoneura with or Streptoneura with a pair of gills. only one gill. =Genus= _Patella_, the Limpet, _Littorina_, the Periwinkle, with gills obliterated, or Shore Shell. and only indirectly represented; breathing is performed by folds of the mantle. =Species= _Vulgata_, the Common _Littoralis_, the (Yellow) Limpet. Periwinkle that lives above low-tide-mark. CHAPTER III CLASSIFICATION, OR THE SORTING OF THE ANIMAL KINGDOM Give a child a few handfuls of shells. Probably the first thing he will do with them is to sort out the various kinds and separate them from one another. Each will go into a little heap by itself; and next, our young friend will find names for them. These are Cap-shells and those Sword-shells; these Saucers and those Plates; these Yellow-shells and those Pink-shells--according as some special character or form or colour strikes his fancy. Now this is what zoologists have been doing with the animal kingdom from the earliest days of science; trying to recognise each distinct kind of animal form, and to give it a name of its own. Unfortunately for the reader, zoologists have been obliged to choose names of Latin and Greek origin, and therefore in writing about animals we are often obliged to burden our pages with long words. This is a disadvantage, but it is a very slight one compared with the great advantage gained by using the learned tongues, which consists in this, that learned men from all countries of the globe can equally understand the names thus brought into use. One particular kind of creature may have one name in English, another in French, another in German, and so on; but the learned world does not trouble itself with this multiplicity of names--it gives the creature a couple of names in Latin, and these names stand good for learned readers in every part of the globe. The importance of this will be fully realised when, in a later page, we shall have to speak of the work done by zoologists, and the way in which they do it. Meantime we must ask our readers to have patience if now and then some long names must be used. These learned names sometimes convey a description of some important characteristic possessed by the animal, and sometimes they are merely fanciful names, such as the child we have spoken of gives to his zoological playthings. It does not greatly matter whether the name is descriptive or not; zoologists describe each animal kind in its most minute details, and the most commonplace or inappropriate name serves its purpose quite efficiently as a means of referring to published descriptions.