OSTRACODA 107 



mantles of adult individuals and developing into the so-called 

 complemental males. 



Certain Cirripedes, viz. certain species of Scal'iielhim and 

 Ihla. 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 

 can be divided into several families, differing slightly in habits 

 and in structvu'es correlated with tliose 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 

 liy means of the two pairs of uni- 

 vamous pediform antennae which move 

 together and in a vertical straight line. ym. 7 i.~ Candona reptans. A, 

 Tn the Cypridae (Fig. 74) there are. Natural size ; B, x 15. «, 1st 



. Til • f antennae ; h, 2nd antennae ; 



ijesides the mandibles, two pairs ot 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 



' Glaus, J'liffrsucJiani/rii, -.ur Brfd/sr/ntnij iks Or ustaceensy stems, Wien, 

 1S76. Brady and Nonaan, " Monograph of the ]\larine and Fresh-Water 

 Ostracoda of the N. Atlantic," Trans. R. Duhlin Soc. (2) iv., 1889, p. 63. 

 Miiller, Fauna unci Flora G. von Xcapel, Monogr. xxi., 1S94 ; " Dentschlands 

 Siisswasser-Ostracoden," Chun's Zoolocjim, xii., 1900. 



