206 Arthropoda. Class 1. Crustacea. 



are sometimes like the hermaphrodite individuals in structure, in 

 other cases they are very degenerate. The eggs are cemented 

 together into large ovigerous lamellee and remain in the 

 mantle-cavity, until the larvae are developed. 



The Cirriped leaves the egg as anauplius of the usual kind, 

 which after moulting acquires the so-called cypris form; the 

 name indicates a certain resemblance to Cypris (Ostracoda). In this 

 state, during which the animal, just as in the nauplius state, is 

 free-swimming, the first pair of antennee is well developed, and has 

 an adhesive disc on the penultimate joint; the second antennae have 

 vanished, but six pairs of thoracic limbs are present, and resemble 

 those of the Copepoda ; besides the nauplius . eye, there is a pair of 

 large compound lateral eyes, and a bivalve carapace 

 surrounding the body. After a time the organism attaches itself by 

 the antennae, the secretion of the oemeot-gland flows through them, 

 and fixes the animal permanently to the spot selected. The large 

 eyes atrophy, though the unpaired eye remains ; the swimming legs 

 gradually change to cirri, their rami increasing in length, and 

 by a series of modifications, the animal attains the lepas or balanus 

 state. 



All the Cirripedia are marine. 



1. The LepadidiB (Barnacles) are provided witt a longer or shorter ped- 

 uncle ; the mantle with five (or more) valves. Many attach themselves to some 

 object which floats in the sea (ships, floating pieces of pumice-stone, etc.) ; this 

 happens, e.g., in the genus Lepas, whose five calcareous valves cover almost the 

 whole surface of the mantle. Others, e.g., Scalpellum (like the PolUcipes 

 figured in Fig. 168 B), with numerous valves and with complemental males, 

 attach themselves to unmovaUe objects, generally at great depths. 



The genus Lithothrya, which bores holes in chalk and coral by means of deli- 

 cate chitinous spines projecting from the very thick peduncle, belongs also to the ' 

 Lepadidse ; and, further, the very different genus Alcippe, with distinct sexes (the 

 female has only the first, fifth, and sixth pairs of cirri, the male is a dwarf with- 

 out a- digestive tract, etc.), bores holes in dead gastropod shells. A peculiar 

 parasitic Barnacle, Anelasma squalicola, is found embedded in the skin of 

 certain Sharks, firmly attached by delicate branched threads which arise from 

 its peduncle. The cirri are without setse (recalluig the limbs of certain parasitic 

 Copepoda), the mantle destitute of calcareous plates. 



2. The Balanidse (Sea-acorns) are sessile, and possess a shell, formed 

 usually of a single circle of plates, with an operculum, which consists of four- 

 valves, and has a median slit (see above). Here belongs the genus Balanus, 

 often occui-ring in great numbers on large stones on the sea-shore, where the 

 animal is sometimes covered with water, sometimes uncovered. Other genera 

 are found upon the Turtle, or on the skin of the Whale (with the lower end 

 beneath the epidermis ; Coronula, and others). 



3. The Bhizocephala, which are modified in correlation with a parasitic life, 

 fonn the most peculiar division of the Oirripedia, and, if the adult alone were 

 examined, would seem to be far removed from the typical members of the order. 

 The body is divided into two regions : an anterior, consisting of much-branched 

 threads, imbedded in the body of the host, and a posterior, sac-like part, which 

 hangs outside the host, and is in connection with the front part by a short 



