286 NATURAL HISTORY. [cH. XXI. 



has been recently published, and which we have re- 

 peatedly noticed. They are of minute size, and are 

 found fixed upon the gills of the lobster, beneath the 

 sides of the shell, often in considerable numbers. 

 The shape of this little animal is very extraordinary ; 

 it, in fact, somewhat resembles a butterfly, with four 

 extended wings, but destitute either of head or ab- 

 domen. On examining it, however, more minutely, 

 a very diminutive abdomen is seen, composed of four 

 joints, and terminated by several bristles ; the head 

 seems pushed between the shoulders, and is provided 

 with a pair of small eyes and two antennae ; the 

 organs of the mouth consist of a pair of claws and 

 four pairs of cleft articulate feelers, serving also, as 

 it would seem, as organs of locomotion in the earlier 

 state of the creature's existence, previous to its be- 

 coming fixed to the branchiae of the lobster, as there 

 are no other locomotive organs. The sides of the 

 body are greatly dilated, forming, in fact, the two 

 anterior appendages, which have been likened to the 

 forewings of the butterfly; the hinder pair of wings 

 is represented by a pair of large oval sacs, dis- 

 tended by eggs. The entire length of the body of 

 this curious little creature does not exceed l-24th 

 of an inch. It is a singular subject for inquiry, how 

 this small animal, unprovided as it almost appears 

 to be with locomotive organs, can attain its singular 

 situation within the body of a large active creature 

 like the lobster. All the individuals yet discovered 

 have been females, having the sacs distended with 

 eggs ; and it is suggested, among other interesting 

 speculations, that it is in a very young state, before 

 the oviferous sacs have attained their distended size 

 (at which latter period the animal seems quite desti- 

 tute of motion), that the Nicothoe astaci (by which 

 name this parasite is designated) possesses more 

 extensive locomotive powers, and is enabled, from 

 its small size, to find its way to the interior of the 

 shell of the lobster. 



