THE EVIDENCE FROM DEVELOPMENT. 



209 



Still more marked is this modification in other fish-lice (Adheres and 

 LernoefR) which resemble Cyclops as closely as does Lernoeocera, 

 but which, sooner or later, become worm-like or otherwise degraded. 

 The suppositions, entertained by competent authorities, firstly, 

 that the fish-lice (Fig. 123) and water-fleas of the Cyclops-type 

 (Fig. 1 1 6, A) have sprung from the same stock; and secondly, that 

 the fish-lice are simply Cyclopean beings degraded by the adoption 

 of parasitic habits, are therefore fully warranted by a consideration of 

 the plain facts presented to us in their development Or once again, 

 to state a cardinal proposition of Evolution the passing development 

 of individuals repeats and reproduces, with modifications, the fixed 

 and past development of the race and class. 



To trace in full the record of Crustacean development would 

 considerably exceed the limits which the patience of the reader might 

 bear, and would unnecessarily protract and repeat facts already 

 exhibited and illustrated by the life-histories just recorded. It might 

 be highly profitable, for instance, to trace the development of those 

 peculiar Crustaceans, the King Crabs or Limuli (Fig. 124), which, as 

 living forms, stand well-nigh alone in their class, and remain con- 

 nected with other Crustaceans only as the leaves on the extremities 

 of one branch of a tree may be said to be 

 connected with those at the tip of another 

 and widely divergent bough. These crabs at 

 one stage of their development, and before 

 leaving the egg within which all their notable 

 features are acquired present a most remark- 

 able resemblance to certain of those singular 

 fossil crabs the Trilobites (Fig. 125), (Prest- 

 wichia), and likewise at another stage to the 

 larva of certain other Trilobites (Trinudeus). 

 This resemblance is well seen on comparing 

 the larva of the King Crab (Fig. 126, B) with 

 the larval Trilobite (A); and still more striking 

 is the resemblance between the King Crab at a 

 later stage (Fig. 127) and the adult Trilobites 

 (Fig. 125). Thus, whilst the Trilobite-race 

 and their neighbours (Eurypteridd) of Silurian 

 age have died out of existence, the King 

 Crabs, springing presumably from the same 

 root-stock, have undergone modification as 

 descent proceeded along " the files of time," and remain to present a 

 crab-race of an age and type, compared with which our existing crabs 

 are but as creatures of yesterday. So also we might, did space 

 permit, strive to show that those curious creatures, the Brine Shrimps 

 (Artemia [Fig. 128, #]) of the Lymington salt-pans and the Great Salt 



FIG. 124. KING CRAB. 



