THE EVIDENCE FROM DEVELOPMENT. 



a 



FIG. 128. BRINE SHRIMP AND YOUNG. 



ing the Crabs (Fig. 115), Lobsters, Shrimps, Prawns, &c., as their 

 typical representatives, present us with a sufficiently diverse group 

 of beings viewed as adults, and likewise afford illustration of equal 

 diversity in their development. 

 Such diversities may be well 

 observed in the comparative 

 study of the early history of 

 such a series of forms as is 

 presented by the lobsters and 

 crayfish, by certain shrimps, 

 and by the common crabs. 

 In its development, the cray- 

 fish apparently presents but 

 little that is remarkable, as 

 compared with Crustaceans 

 of lower nature. Both cray- 

 fish and lobster come from 

 the egg (Fig. 129, a) in the essential guise (b, c) of their species or race ; 

 and the free-swimming "Nauplius-stage," so universal amongst lower 

 Crustaceans, is apparently unknown in their life-histories. There is 

 clear evidence, at the 

 same time, to show that 

 a " Nauplius" condition 

 is represented in their 

 egg-development, and 

 that this phase is ob- 

 scured and modified, 

 presumably through 

 those causes and con- 

 ditions which have 

 placed the lobster and 

 crayfish amongst the 

 aristocracy of the Crus- 

 tacean class. Speaking 

 of the development 

 of the Crayfish and 

 of its Nauplius-stage, 



Huxley says, that animal " is wholly incapable of an independent 

 existence at this stage, and continues its embryonic life within 

 the egg-case ; but it is a remarkable circumstance that the cells of the 

 epiblast (or outer layer of the developing body) secrete a delicate 

 cuticula, which is subsequently shed. It is as if the animal symbolised 

 a Nauplius condition by the development of the cuticle, as the foetal 

 whalebone whale symbolises a toothed condition by developing teeth 

 which are subsequently lost and never perform any function." 



p 2 



FIG. 129. DEVELOPMENT OF LOBSTER. 



