722 



SCIENTIFIC RECREATIONS. 



the butterfly being tipped, or knobbed. The silkworm belongs to this 

 family. These insects undergo complete metamorphosis. The remaining 

 two orders of insects include the house-flies and gnats ; and the flea, and 

 jigger, or chigo, which penetrates the skin and lays its eggs in the flesh, 

 causing thereby dangerous inflammation. 



CRUSTACEA. 



This class includes a number of familiar animals such as the barnacle, 



the crab, the lobster, shrimp, etc.; 

 and curious as it may appear are 

 closely related to our spiders. Their 

 cases or coverings are all articulated 

 or disposed in distinct segments. 

 They breathe through gills or by 

 tubes, and possess legs, or appendages 

 for walking, eating, or guidance. 

 They are generally marine creatures. 

 The shell of the Crustacea is 

 composed largely of lime, and of 

 course becomes very hard in time. 

 It is formed from the skin. The 



of an in^rf i<; mm 

 OI an InSCCt IS COF 



Fig. 854. Crustacea. i. Lobster (Astacns marimis); 2. \^r\(\-i r \\\rt* 

 Cray-fish (Astacns JJuviatilis) ; 3. Crab (Cancer fagurtts) ; DOaV J 11KG 

 4. Shrimp (Cranzonvulsaris); 5- Prawn (Patemon terrains). posed Q f J iead> thorax, and abdomen, 



divided into twenty-one segments, of which seven occupy the head, seven the 

 thorax, and the remainder the abdomen. Twenty segments are furnished with 

 legs, or feelers, or claws a pair to a segment. The lobster or crayfish will 

 give excellent examples of the anatomy of the macrura or lobster kind of 

 Crustacea. The heart is situated in the back. 



The following table given by Professor Nicholson will explain the 

 "segments and appendages" of the lobster : 



Head 



1st Segment Eyes. 



Thorax - 



Abdomen 



I esser antennas. 



Greater antennae. 



Pair of biting jaws. 



First pair of chewing jaws. 



Second pair of chewing jaws. 



First pair of foot jaws. 



Second pair of foot jaws. 



Third pair of foot jaws. 



First pair of legs (claws). 



Second pair of legs (small claws). 



Third pair of legs (small claws). 



Fourth pair of legs. 



Fifth pair of legs. 



Ground appendages. 



Swimmerets. 



Large swimmerets. 



No appendages (tail fin.). ' 



