402 INVERTEBRATE MORPHOLOGY. 



that, on the assumption of a sessile life hermaphroditism became character- 

 istic of the order, the bisexualism of these boring forms being secondarily 

 acquired. The fact that the pigmy males present larval characters sug- 

 gests the idea that their occurrence may be an extreme case of proterandry. 

 If in the hermaphrodite forms it is a rule that the spermatozoa mature 

 earlier than the ova, thus preventing self-fertilization, it is conceivable that 

 this early maturation of the testes might be carried back almost to the 

 Cypris stage and pigmy males be thus developed. 



Not unfrequently barnacles choose the bodies of other 

 animals upon which to fasten, as for instance upon the cara- 

 pace of Limulus, or on the skin of whales, and the genus 

 Anelasma fastens itself upon the surface of the body of a 

 Shark, its stalk penetrating into the tissues and developing 

 rootlike processes and so enabling it to lead a parasitic life. 

 As a result of this the calcareous plates cease to develop, 

 the mantle having merely a leathery consistency and the 

 mandibles and maxillae remain rudimentary. This degenera- 

 tion is carried still further in Proteolepas (Fig. 182), which 



lives as a parasite in the 

 mantle-cavity of other Cir- 

 -vs r hip ec j s ailc | uas a maggotlike 



appearance, the body being 

 distinctly divided into eleven 

 segments and lacking all 

 traces of a mantle. The 

 mouth-parts are modified so 



as to be suctorial, and the 

 FIG. 182. Proteolepas (from BRONN). , . . , . , 



thoracic teet are entirely 

 m = muscle. .. -, -, -, ,. " 



wanting, while the digestive 

 ov = ov;iry. 



vs = vesicula seminalis. tract becomes rudimentary. 



Finally, a group of forms, 



known as the IZhizocephala, fasten themselves to the abdomen 

 of crabs and become transformed into cylindrical or saclike 

 structures entirely destitute of digestive tract and appendages, 

 rootlike processes arising from the anterior end of the body 

 and traversing the body of the host, by whose juices the 

 parasite is nourished. The genus Sacculina consists of an an- 

 terior short cylindrical portion from the extremity of which 

 the rootlike processes arise and which perforates the integu- 

 ment of the host. From the base of this a circular fold arises 



