RHIZOCEPHALA. 221 



C. Rhizocephala. 



The free-swimming stages of the Rhizocephala (NaiqjUus or Cypris 

 stage) were early observed by Fr. Muller (Xos. 54 and 55), 

 KossMANN (No. 49), and others. The later transformations, on the 

 contrary, which bring about the transition from the Cypris stage 

 to the parasitic form, were first observed by Delage (No. 41) in the 

 case of Saccuiina carcini. We shall, therefore, in our description, 

 follow the statemezits of Delage. 



The Nauplius of Saccuiina carcini leaves the egg with a more or 

 less compact form, but by a moult which follows soon after hatching 

 attains a greater length (Fig. 107 A). Otherwise it shows the normal 

 Cirripede type. The two frontal horns with their glands {gl) are 

 well developed, as also are the filamentous frontal organ (/s) and the 

 Nauplius eye {ua), lying close to the brain. As a remains of the 

 labium a projection is found which is known as the rostrum ; on 

 the other hand, the oral aperture, the intestinal canal, and the anal 

 aperture are wanting. The intestinal canal is here replaced by a 

 large accumulation of food-yolk. The Nauplius limbs (/, 2, 3) are 

 developed in the typical manner, but the protopodites of the two 

 posterior pairs are without the masticatory hooks usually found on 

 them. A median mass of cells lying within the body between the 

 brain and the rostrum is assumed by Delage to be the ovary [ov). 



Fritz Muller asserted the presence of a broad, oval, dorsal shield in the 

 Nauplius of Saccuiina. Kossmann, however, has pointed out that Muller's 

 figures are of larvae about to undergo ecdysis, in which the Nauplius cuticle is 

 no longer in contact with the body. 



The most important change found after a third moult is the 

 further growth of the thoraco-abdominal region of the Nauplius, 

 in which the six thoracic segments, with the rudiments of their 

 limbs, soon appear distinct from the abdomen. At the same time 

 the most anterior limbs be^in to assume the character of the adhering 

 antennae [Metanauplius stage). 



By the fourth moult the free Cypris stage (Fig. 107 B) is reached. 

 In this moult the biramose limbs of the Nauplius stage are entirely 

 cast off, and not only do the chitinous envelopes of these limbs 

 adhere to the cast skin, but it appears that even some of the soft 

 parts are thrown off in the moult. The Cypris stage in which, as in 

 the former stages, there is no trace of an alimentary canal, closely 

 resembles in form the similarly-named stage in the Thoracica. The 

 bivalve shell has almost the same shape ; the segmentation of the 

 thorax, the form of the swimming limbs (I-VI) are in agreement. 



