374 



COMPARATIVE ANATOMY 



CHAP. 



feet. This position deserves special notice, because the sexual apertures in no other 

 Crustacean lie so far forward. 



In the Ehizocepliala (Fig. 248) the ovaries, in the shape of two lobate united 

 masses, fill the greatest part of the visceral sac of the body which corresponds with 

 the head of other OirripecUs. They open on each side into an atrium {at), into which 

 the cement glands {dd) also enter, and which itself opens into the brood cavity (S/i). 

 The ovary in Saeculina is said at its first appearance to be unpaired. 



The testes in the Balanidu: and Lrpadidce (Fig. 205, t) occur as two richly-branched 

 tubes at the sides of the intestine and are continued as 2 vasa deferentia, which swell 

 out into sperm vesicles before uniting at the base of the cirrus at the extreme posterior 

 end of the body to form the common ductus ejaculatorius. The 2 testes of the 

 lihhocqiJiala (Fig. 248, t) are simply tubular, and their vasa deferentia emerge at 



Fic. 249.—^, female, B, male genital apparatus ot Asellus aquations (after 0. Sars). 

 Ovary ; ml, ovkUict ; (, testicle lobes ; vd, vas ileferelis ; pi, 1st and 2d pairs of jjleopoda. 



that part of the brood cavity where the visceral sac is produced into the stalk. See 

 also below as to the sexual relations in the C'irrlpedia. 



There is much more uniformity in the genital organs of the Malacostraca than in 

 those of the Entomosiraca. 'While the two ovaries and the two testes remain sepa- 

 rate in the Lejptostraca and Arthrostraca, in the Thoracostraca, with few exceptions, 

 they are joined above the intestine by an intermediate piece. 



Lcptostraea. — The ovaries and testes are long tubes which in the sexually mature 

 animal run dorsally at the sides of the intestine from near the masticatory stomach 

 to the last abdominal segment. The two short sperm ducts of the male emerge 

 in the manner typical of the Malacostraca on a projection on the basal joint of the 

 8th pair of thoracic feet. The aperture of the oviduct also probably lies, as in other 

 Malacostraca, in the third thoracic segment from the last. 



Arthrostraca. — The testes and ovaries are nearly always simple paired tubes 

 which sometimes run through the largest portion of the thorax and abdomen, some- 



