CIRRIPEDIA. 



19 



when separated from the rest of the body, and Fritz Muller says that a parasitic isopod 

 frequently eats the body of the root barnacle and then settles down and draws his 

 nourishment through the roots, which under this stimulus continue their growth. The 

 effect of the root barnacles upon their host is to entirely prevent the normal action of 

 the reproductive organs. 



ORDER IV. CIRRIPEDIA THORACICA. 



These forms agree, in having six thoracic segments, usually bearing six pairs of 

 appendages, the abdomen being absent or rudimentary, the 

 body enveloped in a carapax, which is frequently stiffened by 

 a deposit of salts of lime, and are either sessile or mounted on a 

 fleshy stalk or peduncle. This order embraces the great majority 

 of forms and is readily divided into three families : the Lepadidae, 

 Verrucidae, and Balanidae. 



FAMILY LEPADIDAE. -These Barnacles are characterized by 

 the possession of a fleshy stalk or peduncle which in some is 

 very short, in others sometimes over a foot in length. The 

 capitulum is always flattened and the two sides are drawn to- 

 gether by a single transverse muscle. The general characters 

 of the family have already been mentioned in connection with 

 the account of Lepas fascicularis, and need not be repeated 

 here. Most of the Lepadidas are attached only by the tip of the 

 peduncle, the rest of the body hanging freely in the water, but 

 in the genus Lithotrya a different habit is noticed. The 

 species of this genus, which are mostly tropical, bore holes in 

 shells, corals, or calcareous rocks, in which they live. These 

 holes are excavated by horny spines and calcified beads upon 

 the extremity of the peduncle, and so far as the evidence goes 

 the boring is simply a mechanical action. One species, L. 

 dorsalis, inhabits the Carribean region, the rest living in the 

 eastern seas. 



Pollicipes seems to be the most generalized type of Barna- 

 cles, a fact which is in full accord with its geological history, it 

 being the oldest genus. The calcareous valves are very numer- 

 ous, varying in number from eighteen to over one hundred. 

 Two species occur on the western coast of our continent, 

 P. polymerus being the common California form. Of Ibla 

 and Scalpellum we have already had occasion to speak in 

 connection with the reproduction of the Barnacles. A single 

 species of Scalpellum, S. /Stromei, has been found in the deep 

 waters off the New England coast. There are several genera 

 of Lepadidae in which the calcareous valves of the capitulum 

 are very small or wanting, of which we can only mention Coit- 

 choderma aurita, which has two tubular earlike appendages 

 on the capitulum, which possibly are of use in respiration, 

 while the more common C. virgata is without such append- 



ages. 



The specimen figured (Fig. 25) is attached to a Penella, 



PIG. 25. A Barnacle, Con- 

 choderma virgata, attached 

 to a sea pen, Penella filosa, 

 which in turn was parasitic 

 on a sun-fish. 



