84 THE LIFE OF CRUSTACEA 



side behind. The later development is very unlike 

 those which have been described above, for after a 

 series of nauplius stages the larva passes suddenly, 

 at a single moult, into a stage in which the body 

 and limbs are enclosed in a bivalved shell (Fig. 35, B). 

 From the superficial resemblance of the shell to that 

 of an Ostracod, this is known as the cypris stage. 

 Through the valves of the shell a pair of large com- 

 pound eyes can be seen, as well as six pairs of 

 two-branched swimming feet, while in front a pair 

 of antennules project between the valves. On each 

 antennule is a sucker-like disc by means of which 

 the larva, after swimming freely for some time, 

 attaches itself to a stone or some other object, where 

 it remains fixed for the rest of its life. A cementing 

 substance produced by a gland at the base of the 

 antennules attaches the front part of the head firmly 

 to the support ; the valves of the shell are cast off, 

 and replaced by the rudimentary valves of the adult 

 shell ; the six pairs of swimming feet grow out into 

 tendril-like cirri ; the compound eyes disappear, and 

 the animal assumes the structure of the adult. 



The parasitic Rhizocephala have a very remark- 

 able life-history, which will be described in a later 

 chapter ; but it may be mentioned here that their 

 free-swimming larval stages resemble very closely 

 those of the ordinary Barnacles. It was the dis- 

 covery of this fact which led to its being recognized 

 that the Rhizocephala are highly modified and 



