468 CRUSTACEA MALACOSTRACA. 



The Hemitropha are in the adult provided with a large 

 number of thin hepatic tubes, but in the larva, as also in the 

 Mysidae, the number is smaller (5 or fewer pairs). There are no 

 paired rectal diverticula. 



An antennal excretory gland opening at the base of the second 

 antenna has been recognized in My sis. 



The heart is tubular, with a slight anterior enlargement (cf. 

 Stomatopoda) in Mysidae, but in the Hemitropha it is short 

 and capsular, and situated in the hinder part of the thorax. 

 Two or three pairs of ostia. are present in either case. 



Respiratory organs. In the Lophogastridae and Mysidae a 

 simple elongated or ovate epipodial lobe is borne by the first 

 thoracic legs, but the other thoracic legs in the Lophogastridae 

 and also the thoracic legs of the Hemitropha bear subdivided 

 gills. 



The character of the gills differs considerably in the two families. In 

 the Lophogastridae they each consist of a group of three or four bipinnate 

 tufts, the segments of which are again pinnatifid, springing close together 

 from the outer side of the arthrodial membrane of the seven posterior 

 thoracic legs. They are therefore arthrobranchiae. Moreover in 

 Gnathophausia a small setose lobe is also present arising from the basal 

 segment of the limb, and is regarded by Sars as an epipodial structure. 

 In the Hemitropha the gill is a branched rachis, the branches of which 

 bear simple digitate lobes, and it is a podobranchia, springing from the 

 outer side of the protopodite. In this family the size and the number 

 of the branches of the gills increase from before backwards. 



In the Mysidae there are no gills, unless in the genus Siriella, in 

 which peculiar curved lobes, possibly of respiratory function, 

 are borne on the endopodites of the abdominal appendages of the 

 male. The appendage of the maxilliped found in this family and 

 in the Lophogastridae, is during life kept in constant motion, 

 and perhaps rather subserves respiration by means of the cur- 

 rents so set up over the surface of the body, than itself 

 directly effects it. 



The oviducts open as usual at the base of the sixth thoracic legs. 



In accordance with the differences in the condition in which 

 the young are hatched, a brood pouch is present in the Holo- 

 tropha, but absent in the Hemitropha. It consists of lamellar 

 processes (oostegites) from the bases of the two (Mysis) to 

 seven (Lophogastridae) posterior thoracic legs. 



In the Hemitropha the eggs are contained until hatching in 

 a median or paired ovisac secreted by the oviducts. The 



