igoS] , EXCRETORY ORGANS OF METAZOA. 585 



small groups of gland cells, that take up carmine, placed at the bases 

 of the maxillipeds, thoracic and abdominal extremities. Similar ap- 

 pear to be the " Segmentalorgane " of the Ostracoda (G. W. Miiller, 

 1894), which in Paradoxostoma lie above each leg pair, and in 

 Bairdia above the first pair; and the glands opening on the maxil- 

 lipeds of Cyprids (Claus, 1890). 



Genital Ducts. — The first origin of these seems to have been 

 little investigated, but Pedaschenko (1899) finds them to arise from 

 a proximal mesoblastic and a distal ectoblastic portion. 



Homologies of the Preceding Organs. — The maxillary, antennal 

 and maxillipedal glands are probably homodynamous, and seem to 

 differ only in antero-posterior position. Sometimes they occur at 

 the same time in the same individual, or (as in Phyllopods and 

 Copepods) the antennal gland is the larval and the shell gland the 

 adult excretory organ. Sometimes both antennal and shell glands 

 are absent in the adult, as in some Copepoda (Nemec, 1896). Waite 

 (1899) has discussed these homologies at some length, and resumes: 

 " The nephridium of Annelids is probably represented in Crustacea 

 in the second (antennal) segment by the antennal gland of Alala- 

 costraca; in the fifth (second maxillary) segment by the shell gland 

 of Entomostraca and some Malacostraca ; in the sixth (first maxil- 

 lipedal) segment of some Malacostraca by the ' Segmentalorgan ' of 

 Lebendinski ; it is possibly represented in the fourth (first maxillary) 

 segment by the excretory organ described by Boutchinsky, and in 

 the sixth to thirteenth (maxillipedal and pareiopodal) segments in 

 part by the branchial glands, and in part (in the eleventh and 

 thirteenth segments) by the genital ducts." 



Nephrocytes. — Bruntz (1903) has found these excretory cells 

 to be distributed as follows : they are absent in the Cladocera ; there 

 is one cephalic pair in the Isopoda, Amphipoda and Cirripedia ; up 

 to eight pairs placed in the thorax in the Schizopoda, Decapoda (in 

 the gills), and Copepoda parasitica (diffuse) ; from one to eight 

 pairs in the abdomen in the Isopoda and Stomatopoda (in the legs) ; 

 and eleven pairs in the thorax and abdomen in the Amphipoda. 



Other Excretory Organs. — As such have been described the fer- 

 ment cells of the liver of Decapoda, Amphipoda and Isopoda, and 



PROG. AMER. PHIL. SOC, XLVH. I90 LL, PRINTED JANUARY I4, I909. 



