36 THE CRUSTACEA 



process forming the front of the head (Fig. 18, a). In the males 

 of some Cladocera they form clasping organs for holding the female. 

 The antennae difier very much in the various orders. In the 

 Notostraca they are vestigial (Fig. 20, A, a") and may even be 

 absent in certain species of Apus. In the males of the Anostraca 

 they are converted into powerful claspers for seizing the female, 

 and may assume extraordinary and complex forms. A pair of 

 filaments, known as frontal apj^endages (Figs. 21 and 32, /.«), 



arise, in many Anostraca, from the base 

 of the antennae, though sometimes they 

 are inserted on the front of the head 

 and seem quite unconnected with the 

 antennae. They may coalesce at the 

 base, and may be more or less ramified, 

 adding to the complexity of the apparatus 

 carried by the male. In the females the 

 Head of chirocephaias diaphanus antennae are much simpler in form, and 

 (Anostraca) viewed from in front, ^^e probablv purely seusory in function. 



(After Simon.) a', antennule ; a", -t^ e /~^^ > i 



antenna ; /.«, frontal appendages, It WOUld SCCm f rom ClaUS S observations 



which in tliis species are large and ^i i i j_ i> n 7 • j_i >. 



branched. ou the development 01 hranckipus that 



the endopodite of the antenna atrophies, 

 and that the whole appai\atus of the adult develops from the 

 protopodite and exopodite of the larval antenna. 



In the Conchostraca and Cladocera the antennae are large 

 biramous swimming - organs. In the former group they have 

 multiarticulate rami, and they are protruded ventrally between the 

 valves of the shell (Fig. 17). In the latter order the rami have 

 few segments, and, since the head is not enclosed between the 

 valves of the shell, the antennae project freely (Fig. 18). In 

 the genus Laiona (Cladocera) a large process from the proximal 

 segment of the exopodite causes the antenna to appear as if three- 

 branched. 



The mandibles (Fig. 8, C, p. 12) are devoid of palps in all existing 

 Branchiopoda with the exception of Polyartemia, in which a vestigial 

 palp has recently been found by Ekman. As a rule, they have 

 broad toothed triturating surfaces, but in some predatory Cladocera 

 (Leptodora) they become long sickle-shaped blades. 



• The maxillulae (Fig. 22, A) are of small size and simple form. 

 As a rule, each consists of a single lobe armed with spines on 

 the inner edge. In the Notostraca they seem to consist of two 

 lobes, but it is possible, as Claus suggested, that the inner and 

 anterior lobes represent the lower lip, or paragnatha, otherwise 

 wanting in the group. 



The maxillae (Fig. 22, B) are also greatly reduced and consist of a 

 simple lobe. In the Cladocera they are entirely wanting in the adult, 

 but a distinct rudiment is present in the embryo. In the Notostraca 



