IO4 Invertebrata. 



can be seen, by the aid of the microscope, actively 

 darting about ; these are representatives of a fourth 



sub-class. They are all 

 FlG - s8. minute at the present 



day. Certain forms 

 bear gill processes ap- 

 pended to their feet, 

 and hence are known 

 as ' gill-footed ' or Bran- 

 chiopods. Many close- 

 ly allied species have 

 the dorsal wall extend- 



Cyclopsquadricornis carrying its egg sacs. e( J j n the form of an en- 

 o. he small figure is the Nauphus or larva. 



veloping shell, just like 

 the gill-covering laminae in the lobster. 



Those crustaceans which are parasitic are closely 

 related to the water fleas, and undergo retrogression 

 until they become reduced to little sacs with bristles 

 for jaws, with sucker-like fore feet, and often with no 

 trace of segmentation (fig. 59, A). Some live on the 

 bodies of larger crustaceans such as lobsters, others 

 on tunicates, but they are mostly found attached about 

 the gills of fishes. The early stages of .these are little, 

 free, marine larvae with developed jaws and a moderate 

 post-abdomen (fig. 58). Many non-parasitic species 

 remain for their whole life in a state like that of the 

 larvse of these parasites. 



In all these lower crustaceans the earliest stage 

 of existence after emission from the egg is in the 

 form of a minute oval body with three pairs of limbs 

 and one central eye. This is known as a Nauplius, 

 and it assumes its adult form by the growth of new 

 segments and new limbs. The nauplius stage of 



