Vv OSTRACODA 107 
mantles of adult individuals and developing into the so-called 
complemental males. 
Certain Cirripedes, viz. certain species of Scalpellum and 
Ibla and all the Acrothoracica, are dioecious. It is impossible 
to decide at present whether these species retain the primitive 
dioecious condition of the ancestral Cirripedes, or whether they 
too have been derived from an hermaphrodite state, but in the 
present state of knowledge they hardly affect the validity of 
the theory that has been proposed to account for the nature of 
the complemental males and the hermaphrodite individuals. 
Order IV. Ostracoda. 
The Ostracoda are small Crustacea, the body consisting of 
very few—about eight—segments, and being completely enclosed 
in a carapace, which has the form of a bivalve shell. Develop- 
ment is direct, without a Nauplius stage. 
The Ostracoda' are marine and fresh-water animals that 
ean be divided into several families, differing slightly in habits 
and in structures correlated with those habits. 
The Cypridae and Cytheridae include all the fresh-water 
and a vast majority of marine genera, adapted for a sluggish 
life among water-plants, though some can swim with consider- 
able activity. The common Cypris 
and Candona of our ponds and streams 
are familiar instances. The move- 
ments of these animals are effected 
by means of the two pairs of uni- 
ramous pediform antennae which move 
together and in a vertical straight line. yg. 74.—Caundona reptans. A, 
In the Cypridae (Fig. 74) there are, Natural size; B, x 15. a, 1st 
: : : : antennae ; 6, 2nd antennae ; 
besides the mandibles, two pairs of c, walking legs, (After Baird.) 
maxillae, a pair of walking legs, and, 
lastly, a pair of appendages, which are doubled up into the 
carapace, and are used for cleaning purposes. In the marine 
Cytheridae there is only one maxilla, the last three appendages 
' Claus, Untersuchungen zur Erforschung des Crustaceensystems, Wien, 
1876. Brady and Norman, ‘‘ Monograph of the Marine and Fresh-Water 
Ostracoda of the N. Atlantic,’ Yrans. R. Dublin Soc. (2) iv., 1889, p. 63. 
Miller, Fauna und Flora G. von Neapel, Monogr. xxi., 1894; ‘‘ Deutschlands 
Siisswasser-Ostracoden,’’ Chun’s Zoologica, xii., 1900. 
