6 A HISTORY OF RECENT CRUSTACEA 



to run a few steps into the ocean and out again. With a 

 similar effort of the scientific imagination, the illustrious 

 Erasmus Darwin, when a schoolboy, excused himself for 

 eating roast goose during Lent by the scriptural axiom 

 that ' all flesh is grass,' and the goose therefore a species 

 of vegetable. 



Ro far as the name Crustacea implies a covering of any 

 considerable toughness, it is little applicable to some of 

 the parasitic members of the class, but in general much 

 more confusion than advantage follows from the dis- 

 placing of long-established names in the effort after 

 absolute accuracy. If we are never to use the scientific 

 designation of a group unless it exactly applies to all the 

 members of it, then what is to be done, one writer 

 rather maliciously asks, in the case of the species called 

 Homo sapiens ? 



A general though not a complete agreement prevails 

 in regard to the external boundaries of the crustacean class. 

 The proper mode of subdividing it and the arrangement 

 of the subdivisions are subjects still open to much dis- 

 cussion and dispute. Any final decision depends upon 

 questions of genealogy which have yet to be answered. 

 In the mean time four sub-classes may be accepted, under 

 the names Gigantostraca, Malacostraca, Entomostraca, and 

 Thyrostraca. The Gigantostraca, or giant-shells, are the 

 oldest in known lineage, and, as the name implies, fore- 

 most in the average of magnitude. They seem to be 

 tending to speedy extinction. The Malacostraca include 

 forms highest in development and of most direct value to 

 mankind. The Entomostraca probably surpass the rest 

 in multitude of individuals, if not also of species, but are 

 the smallest in average size. The Thyrostraca, commonly 

 called Cirripedia, though they fall short of the Entomostraca 

 in numbers, excel them in bulk, and are even more remote 

 in outward appearance from any general idea of a crusta- 

 cean, such as the better known malacostracan lobster, or 

 the crab fish, might suggest. 



The Greek word Malacostraca, meaning soft-shelled 

 animals, is practically equivalent in sense to the Latin 



