ANNULOSA. 435 



injury; and though themselves perhaps at first wholly 

 invisible, their shadows will be seen with great distinct- 

 ness at the bottom of the basin; and thus many forms 

 which might otherwise escape observation be rendered 

 evident, 



" The microscopic wonders of the sea, however, are still 

 far from being exhausted; it presents as many, if not 

 more, curiosities at the bottom, where its depths are never 

 opened to view, than at the surface. The best and most 

 convenient mode of obtaining these, is by the use of an 

 instrument, with which all perhaps are acquainted in one 

 shape or another, we mean the dredge. The essential 

 qualities of a microscopist's dredge are, a small and con- 

 venient size, with sufficient weight to ensure its sinking to 

 and keeping at the bottom, even when at a considerable 

 depth and drawn with some velocity through the water. 

 The dredge we should recommend is made of cast iron, 

 which reduces the cost considerably; and it is, in practice, 

 found to be sufficiently strong. It is about eighteen inches 

 in length, and the opening is about four inches wide, the 

 two sides diverging outwards at a slight angle, and coming 

 to a sharp edge." 



ANNULOSA. Articulata. The animals composing the 

 sub-kingdom Articulata are characterised by having the 

 body enclosed in a tunic, or integument, consisting of a 

 series of rings, segments, or joints, "articulated" together 

 by a flexible membrane. 



Arachnida. The animals forming the class Arachnida, 

 include spiders and their allies, most of which are looked 

 upon with disgust and aversion by the generality of man- 

 kind. Arachnida are divided into two orders, Trachearia 

 and Pulmonaria. The first includes the Acaridce or 

 Mites, in which we find tracheae, as in insects, but no 

 distinct vascular apparatus: in the second, spiders and 

 scorpions are included, and these have a pulmonary cavity, 

 and a well-developed circulating system. The above are 

 distinguished from Podopthalmia or Arthropoda by their 

 aerial respiration, their possession of four pairs of legs 

 attached to an anterior division of the body, and the total 

 absence of antennae. The body is also covered with a 

 softish skin, which sometimes attains a horny consistency, 

 F F 2 



