CRUSTACEA. 537 



except Stomatopoda, and opening on the basal joint of the second antenna : 

 and in Amphipoda as one or two glands generally said to open into the 

 anterior end of the proctodaeum, but in reality it appears opening into the 

 posterior end of the mesenteron (Spencer). A pair of glandular excretory (?) 

 sacs open close to the anus in Stomatopoda (Claus). 



The sexes are united in the majority of Cirripedia : and in the Cymo- 

 thoidae (Isopoda] the sexual organ of the young animal is male, of the old, 

 female in function. In a few Cirripedia minute cirriped-like ' comple- 

 mental' males are found on the hermaphrodite animal. In Scalpellum 

 vtdgare the male is not like a Cirriped, nor is it in the few instances where 

 the sexes are separate, e. g. Sc. ornatum. In many Copepoda the animal is 

 sexually mature before it is adult. The sexual organs vary much in 

 character ; they may be paired or azygos, and if paired may be united 

 across the middle line, e. g. Decapoda. They lie generally in the thorax, 

 sometimes in the abdomen, e. g. Stomatopoda, Pagurus. The ducts are as 

 a rule double, each with its separate aperture. This aperture is variously 

 placed in the thorax or abdomen in Entomostraca^-, but in the Mala- 

 costraca the male apertures open on the coxae of the last or eighth 

 thoracic feet, the female on the coxae of the sixth, or else on the sterna of 

 the corresponding somites. In the Cirripedia a long penis terminates 

 the abdomen. Accessory glands are rarely present, e. g. the gland which 

 secretes the capsule of the ovisac in Copepoda. Receptacula seminis are 

 occasionally found as in most Copepoda. Parthenogenesis occurs in Artemia 

 and Apus among Branchiopoda ; in the Cladocera (so-called summer ova) 

 and in some Ostracoda (certain species of Cypris z }. The offspring belong 

 to the female sex. In Cladocera males are eventually produced, and this 

 is probably the case in Ostracoda, in Artemia and Apus, but has not been 

 proved to occur. The male generally differs from the female in size, e. g. 

 in parasitic Copepoda where it is minute ; in greater development of organs 

 of special sense ; in the presence of organs modified to retain the female ; 

 or of accessory efferent organs, e.g. the two first pairs of modified ab- 

 dominal feet in Decapoda : and in the absence of special contrivances to 

 retain the ova, e.g. brood lamellae, such as are attached to more or 

 fewer of the thoracic limbs in Arthrostraca and Mysis. 



The spermatozoa are vibratile in Cirripedia : so too in Ostracoda after 

 they have entered the female ducts 3 . In other Crustacea they are non- 

 motile and are in Decapoda furnished with processes. They are generally 

 united into spermatophores either by the secretion of the wall of the vasa 

 deferentia or more rarely of special glands. The ova vary much in size, 



1 The oviducts of Cirripedia open at the base of the first pair of limbs, the most anterior 

 position known in Crustacea. 



2 Cattdona is parthenogenetic in late autumn ; so too Cypris vidua. 



3 The sperm shows amoeboid motion in the Cladoceran Polyphemus, but not in other members 

 of the order. See Zaccharias, Z. W. Z. xli. 1885. 



