444 PHYSIOLOGY OF THE INVERTEBRATA. 



complete, '• and the embryo attains to its earliest larval con- 

 dition within the ^^Q^^ * 



In the Ampliipoda and Isopoda, the male organ consists of 

 a testis, which opens on the first abdominal somite. There 

 are either one or two pairs of penes. The female organ con- 

 sists of two ovarian tubes ; and the ducts open on the ventral 

 side of " the antepenultimate thoracic somite or on the bases 

 of- the limbs of this somite." The ova, after being laid, are 

 deposited in an incubating pouch or chamber, situated 

 " beneath the thorax, enclosed by the oostegites of the 

 thoracic appendages." No true metamorphosis takes 

 place, except in the young of certain parasitic forms. The 

 vitellus in some forms undergoes complete segmentation, 

 whereas in others it is only partial. 



In the Stomajwda the sexes are distinct. The testes- 

 of the male consist of ramified glands, from which pass off 

 two vasa deferentia, which terminate in penes projecting at 

 the base of the last pair of feet. The ovaries consist also of 

 ramified glands, situated in the lateral portions of the 

 posterior abdominal segments. These glands are united in a 

 long tube, which envelopes the alimentary canal. "The 

 portion of the ovary, contained in the three segments to 

 which are attached the ambulatory feet, sends towards the 

 ventral surface three branches, which join, upon the median 

 line beneath the abdominal cord, with those of the opposite 

 side, and form, in the middle of each of these three segments, 

 a round sinus. These sinuses are connected by longitudinal 

 anastomoses, and the anterior one is prolonged into a common 

 papillary vulva, situated in the middle of the first abdominal 

 segment, beneath a homy process." (Von Siebold.) 



The genital organs of the Jinomonra and Brachyura^ differ 

 so little in structure from those of the Macroura, that we 

 describe only those of the latter order, with the addition of a 

 few general remarks on the first two mentioned orders. 



* For further information see Claus' GrunchU'nge der Zoolo<jie; and Dar- 

 win's Monograph of the Cirripedia, z vols., 1 85 1-4. 



