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■Reproductive Organs. 



Ascidians are not divided into two sexes, and conse- 

 quently each individual is hermaphrodite, or possesses both 

 male and female reproductive organs (gonads), although 

 cross - fertilization is probably the rule as a protogynous 

 condition is very general — the female organs maturing 

 before the male. In Ascldia mentida, however, self- 

 fertilization does sometimes take place. The gonads in 

 Ascidia lie close together on the left side of the body, 

 alongside the stomach and intestine (PI. II., fig. 4, gon.), 

 and are provided with delicate ducts (gd.), which open like 

 the intestine into the atrium ; so that the mature ova and 

 spermatozoa are carried out of the Ascidian's body by the 

 current of water flowing from the atrial aperture. In 

 many Ascidians fertilisation and development take place 

 in the atrium, a part of which may be set aside as an 

 incubatory pouch. In some Ascidians (certain Molgulidae 

 and Cynthiidae) reproductive organs are present on both 

 sides of the body, and in others (Pohjcarpa) there are 

 many complete sets of both male and female systems 

 attached to the inner surface of the body-wall, on both 

 sides, and projecting into the peribranchial cavity. 



The ovary in Ascidia mentula is a slightly ramified gland 

 which occupies the greater part of the intestinal loop (PI. 

 II., fig. 4, gon.). It contains a cavity which, along with 

 the cavities of the testis, is derived from an embryonic 

 mesodermal space which has been compared with a coelom 

 but may be merely blastocoelic, and the ova are formed on 

 its walls and fall when mature into this cavity. The 

 oviduct is directly continuous with the cavity of the ovary, 

 and leads forward alongside the rectum, and external to 

 the vas deferens to open into the atrium. 



The testis is composed of a great number of delicate 

 branched white tubules, which ramify over the much 



