208 CRUSTACEA. 



blades have developed, the upper one (endopodite) already showing the formation 

 of a terminal joint. Behind these limbs a new rudiment {My!') can be made 

 out occupying the space between the first maxilla and the first pair of feet ; this 

 is the rudiment of the second maxilla which arises as a curved triangular plate 

 after the first pair of feet has already appeared. The second pair of feet is still 

 wanting, but the posterior end of the body is now marked by the development 

 of two furcal setae. 



The 'fifth larval stage (Fig. 100 B) is distinguished by the further development 

 of the second maxilla (Mx"), which now appears as a four-jointed limb directed 

 backwards and carrying on its basal joint a projecting masticatory blade. It is 

 an interesting fact that these limbs, during the ontogenetic stages of Cypris, 

 not only resemble legs, but function as such, a condition which is retained 

 throughout life in the Cytheridae. The two furcal appendages at the posterior 

 end of the body are now more distinctly marked. Among the internal organs 

 we must mention the development of the hepatic tubes (L), which extend into 

 valves of the shell, and the first appearance of an organ lying below the eye and 

 regarded by Claus as the shell-gland (Fig. 101, SD). 



The sixth stage (Fig. 101) is characterised by the appearance of the last 

 (second) pair of feet (/'"). The second maxilla has become transformed by the 

 increase in size of its masticatory blades and the diminution of its leg-like palp. 

 The anterior pair of feet, until now somewhat undeveloped, has several joints. 

 The posterior (last) pair of feet essentially resembles the rudiments of the limbs 

 which precede it as found in earlier stages. The caudal fork already approaches 

 its adult form and terminates in two strong hooked setae. 



In the seventh stage, which in the structure of the limbs shows the adult 

 condition, the rudiments of the genital apparatus are recognisable. Among the 

 alterations which have taken place in the limbs, the development of a small 

 leaf-like appendage (exopodite) on the basal joint of the second maxilla, and the 

 segmentation of the last pair of feet, deserve special mention. 



In the eighth stage, the development of the genital rudiment progresses, the 

 way being prepared for the development of sexual differentiation, while the 

 ninth and tenth seem to be stages for the development of sexual maturity. 



The Cytheridae, according to Zenker, hatch at a stage more or less 

 comparable with the fourth stage of the Cypridae. Besides the two 

 pairs of antennae, the mandibles and the first maxillae have appeared 

 and are somewhat advanced in development. The rudiments of the 

 two pairs of feet seem to be present behind the above. The 

 mandibular palp still functions as a locomotory organ. 



In Cypridina, whose eggs, like those of the Cytheridae, pass 

 through their embryonic development between the valves of the 

 mother, the shell undergoes changes of shape resembling those 

 pointed out in connection with the young form of Cypris. The 

 compound paired eyes appear early. Embryos just before hatching 

 possessed the furcal pro-appendages, but were without the three 

 posterior pairs of appendages (the first pair of feet, the cleaning foot, 

 and genital prominence). It is probable that the larva leaves the egg 

 nearly resembling the adult in shape (Claus, No. 33). 



