THE CIRRI FED I A 133 



J)nplorbis what appear to be extremely degraded, but still functional 

 male individuals. In this genus the usual testes are absent, as they 

 are also in Sylon, but in the latter no male individuals have been 

 found, and parthenogenesis may perhaps occur. 



DEVELOPMENT OF RHIZOCEPHALA. 



The development has been most fully worked out in the case 

 of Sacculina by Delage, whose results have been confirmed and 

 extended by G. Smith. The larva is hatched in the form of a 

 nauplius (Fig. 82, A) showing a general resemblance to that of 

 the normal Cirripedes, but differing in having no alimentary canal. 

 The fronto-lateral horns are well developed and each contains a 

 pair of gland-cells (gl). A process on the ventral side, called by 

 Delage the rostrum, appears to represent the labrum, but there is 

 no mouth. Posteriorly the body terminates in a caudal furca. 

 The three pairs of limbs have the usual form, but the second and 

 third pairs are without the masticatory hooks found in the normal 

 Cirripedes. Frontal filaments (fs) are present, as is also the un- 

 paired eye (ua) resting on a cerebral ganglion. In the later stages 

 the thoracic somites and their appendages become differentiated 

 within the posterior part of the body, not forming a postero- 

 ventral process as in the normal Cirripedes. 



The Cypris-stage (Fig. 82, B) agrees in all essentials with that 

 of the normal Cirripedes except for the absence of a mouth and 

 alimentary canal, and the vestigial condition of the mouth-parts. 

 The fronto-lateral glands (gl) open in the usual position near the 

 margin of the valves of the shell. The antennules consist of three 

 segments only, and are without any adhesive disc ; the terminal 

 segment bears two appendages which are probably sensory and 

 a backwardly curved filamentous process which is stated to be the 

 organ of attachment. The six pairs of thoracic limbs have the 

 protopodite not distinctly segmented and the exopodite and en- 

 dopodite each composed of two segments. The abdomen (ab) 

 is unsegmented and terminates in a pair of furcal appendages. 

 The unpaired eye persists, but be} 7 ond the muscles for moving 

 the body and appendages no other internal organs are differentiated. 

 It is worthy of note that there appear to be no cement-glands in 

 connection with the antennules. 



After a free-swimming life of three or four days, the Cyprti 

 larva becomes attached to the host. In the case of Pcltogaster, 

 which infests hermit-crabs, it is probable that the larva settles at or 

 near the spot where the adult afterwards appears on the host's 

 abdomen. In Sacculina, which attacks Brachyurous crabs, however, 

 the place of attachment of the larva has no relation to the place of 

 emergence of the adult parasite, the latter being always found under 



