14.'^ 



i\vei!Tei;i:atk animals. 



Crustaceans, which occur in both fresh aud salt water. Tliey are 

 distingui.slieil by the fact tliat the liody is entirely euchjsed in a 

 shell, which is made up of two lateral halves or valves. Tlie valves 



of the shell are united by a 

 niembrane along tiie back, but 

 i-an be ojieneil l)elo\v, so as to 

 allow of the ])i-otrusiou of the 

 fci't. 



Very closely i-elated to the 

 C'ojiejjods is a group of curious 

 Crustaceans, which are often 

 called " Fish-lice " (Ichtlujnph- 

 thii'ii), because in their adult 

 condition they are attached 

 parasitically to the skin, eyes, 

 or gills of tishes. The males, 

 however, are usually free. 



In its parasitic condition (fig. 

 98), the animal is more or less 

 swollen and deformed, its lindis 

 being often rudimentar}', and 

 the segmentation of its body 

 obscured or lost. They are 

 hrndy fixeil, in various way.f, 

 to their hosts, and the females 

 carry large external bags of 

 eggs (ovisars\ Tlie young of 

 levelojicd liiubs and eves, and 



Fig. (IS.— Feiimle of Adilhrrrs 

 iii.l^nili.-.l. Tlie line phnra 

 tlie figure slinw.^i tlic iviil .^ 

 cinineii ; <1 Di-<e of .Tttarlinieii 

 ii|i"ii tlir last pair "f llinrae 



InngsiJr 



(Ivisac. 



the Fish-lice, 

 lead an acti\"( 



i\ve\'er, 

 comotive 



.■i\'e well- 

 L'.xistence. 



i-.lic. 



( MlDF.Il CrRRIFF.m.X. 



The last order of Cnistiicen is that of the CirripriHii (Lat. cirrus, 

 a cui'l ; and /"'.v, foot), Coni|irising the so-called Barnacles and Acorn- 

 shells, bcith extieniely unlike (.'ruslaceaiis to look at. All the Cirri- 

 ])edes arc distingiiislird by the fact that, whilst they are quite free 

 when yonng, .■iiid Nery similar to some of the little ( 'rustaceans jnst 

 (h.'scribed, when adult thi'\' .'ire imnio\';il)ly fixed by their heads to 

 .some Solid object. In this tixed condition the bod}' anil internal 

 organs are, in most c.-isi's, jii-oterted by nie.'ins of a calcareous shell, 

 eomposed of many pieces, anil the only ]ia,rt of \he body which 

 ii'in.iins mo\;ible is Ihe legs, x\-liirli .-ire consiantly thrust cnd^ of the 

 sli'll :iiiil ag;iin dr;i,wii in in i|nest of food. The ( 'irri/jfdiii- were 

 fur )ly ilrseribeil a; " miiUi\;il\'e " sli"ll-tish (.l/n/Zf/.s-iv^), owing to 



