PARASITA. 



239 



€hondracanthidae, on the contrary, we find the above-mentioned abbreviations 

 •of metamorphosis. The young larvae which hatch from the egg of Chondra- 

 ■canthus gibbosus already show behind the Nauplius limbs the rudiments 

 of two other pairs of limbs, and must therefore be described as Metanauplii 

 (Claus, No. 71). The youngest parasitic females remain essentially at the 

 level of development of the first Cyclops stage. Of the four distinct thoracic 

 segments seen at this stage, only the two anterior ones carry bilobate rudiments 

 of limbs without setae, while the posterior region of the body (abdomen) is 

 small and divided into two parts. No further Cyclops forms follow these first 

 •stages, but while the small male remains during life at this grade of develop- 

 ment, the female undergoes a secondary transformation, the region of the third 

 and fourth thoracic segments increases in size and forms the main portion of 

 the body. The large thoracic 

 region now becomes transformed 

 in an extraordinary manner, dorsal 

 and ventral swellings and lateral 

 projections appearing as secondary 

 outgrowths on each of the thoracic 

 segments (except the first). 



Somewhat similar phenomena 

 are found in the family of the 

 Philicthyidae. Here the larval form 

 which hatches from the egg in the 

 genus Lernaeascus is a Nauplius 

 with a large provision of food-yolk, 

 whose second antennae are without 

 masticatory hooks, the adhering 

 apparatus (frontal band) being 

 absent, as in the Metanauplius of 

 Chondr acanthus. The parasitic 

 form arises from a Cyclops stage 

 in which the thorax and abdomen 

 are distinctly segmented, but only 

 the two anterior thoracic segments 

 show a well-developed rudiment of 

 a swimming limb, while the third 

 thoracic segment has only the 

 vestigial remains of a limb. The 

 male retains the shape of one of 



these developmental stages, while the female is parasitically transformed, the 

 thoracic region lengthening, while a peculiar development of asymmetrical rows 

 of chitinous scales makes its appearance (Claus, No. 69). 



In the family just described, the ascending series of larval forms does not 

 appreciably rise above the level of the first Cyclops stage, but in the Dichelestiidae, 

 where the body of the adult undergoes less modification, the later Cyclops 

 stages are also passed through. The young which hatch from the egg are true 

 Nauplii. The frontal band appears to be wanting (?) in the larvae of this 

 group. 



An adhering apparatus of this kind is found in the larvae of the Caligidae, 

 which, in their earlier stages, strikingly resemble the Cyclops stage (pupae) 

 of Lcrnaca (Clatjs, No. 70, see below). The later larvae, which more nearly 



Fig. 113.— Two larval stages of Lernaea branchialis 

 (after Claus). A, first Cyclops stage. B, so- 

 called pupal stage. a\ first antenna ; a", second 

 antenna ; //, first, ///, second pair of thoracic 

 limbs ; k, adhesive mass ; oc, eye. 



