BRANCHIOPODA. 373 



The heart is elongated and segmented in the Phyllopoda (Fig. 

 247), saccular in the Cladocera (Fig. 251 ). Coiled excretory organs 

 known as shell glands (Figs. 248 and 251, s d) from the fact 

 that their coils often lie between the lamellae of the shell, are 

 always present, and in the cases where the duct has been traced 

 (Limnadia and Apus), open to the exterior on the posterior 

 maxillae. The antennary glands, though present in the larvae 

 of Phyllopods (Glaus), are not functional in adult Branchiopoda. 



Respiration is performed by the entire surface of the body 

 the area of which is much increased by the reduplicature of the 

 skin forming the carapace, by the foliaceous swimming feet, as 

 also by their more specialized lobes, the proximal epipodites. 



Reproduction. The Branchiopoda are of separate sexes.* The 

 males are distinguished from the females by the structure of the 

 first pair of antennae which are larger and more richly provided 

 with olfactory hairs, or by the prehensile character of the second 

 antennae (Anostraca), or (Cladocera, Conchostraca) by the 

 character of their anterior swimming feet which are armed with 

 prehensile hooks. In general the males are less frequently met 

 with than the females, and, in some cases only at certain seasons 

 of the year. 



In the Cladocera, and in the genera Apus, Artemia and 

 Limnadia among the Phyllopoda, many generations consisting 

 entirely of females and reproducing parthenogenetically succeed 

 one another. In the Cladocera this is generally the case during 

 the early summer. In the late summer and autumn mixed 

 broods consisting of males as well as females, and broods of 

 males are produced. From the fertilized " resting " or " winter " 

 eggs which are now produced, the parthenogenetic broods of the 

 following year arise. 



Weismann concludes that in the Daphnidae the succession of broods- 

 forming the life cycle is definite for each species, and adapted to its mode 

 of life. Thus in species inhabiting large bodies of water, such as lakes, 

 many parthenogenetic female broods succeed one another during the 

 summer, and it is only on the onset of cold weather in autumn that males- 

 are produced. Species which multiply in puddles on the other hand 

 may present only a single parthenogenetic generation. 



Issakowitsch has recently published f a preliminary account of some 



* The statement which has recently been made, that Apus is hermaph- 

 rodite, does not rest on satisfactory evidence. Hermaphrodite forms 

 sometimes, however, make their appearance in the Cladocera, cf. p. 379. 



| Geschlechtsbestimminde Ursachen bei den Daphniden, Biol. Central- 

 blatt, Bd. 25, No. 16, 1905. 



