66 



A\IAN CESTODES, 



reached their full de% elopinent hy tlie time that the vas deferens 

 and vagina liad established communication with the exterior. 

 Tlie shell-gland was recognisable fairly early as a glandular mass 

 surrounding the inner end of the vagina {sensu lata). 



The vas deferens, cirrus-sac, vagina, and receptaculum seminis 

 persisted in segments containing ripe eggs, though all of these 

 ducts were less prominent than in sexually mature segments. 

 The most persistent of the genital organs were the shell-gland 

 and \ itelline gland, the former, or rather its debris, being seen in 

 fairly ripe segments. The ovary was recognisable for only a 

 short distance posteriorly from the point where the testes had 

 disappeared. 



The uterus originated on the ventral side of the shell-gland 

 complex, and was recognised rather early as a reticulum surround- 

 ing the testes. It first occupied the same area as the testes, that 

 is, the middh^ of the posterior third of the segment. Small etrL'-s 

 were seen lying in the utei'ine reticulum. As these de\eloped 

 and increased in size, the testes dwindled and finally disappeared. 

 The uterus gradually invaded the rest of the parenchyma, passing 

 forwards and outwards below the excretorj^ vessels. Each lolie 

 or pouch of the uterus contained several eggs, and retained its 

 connection, though sometimes very slightly, with the other parts. 

 Tlie formation of separated egg-capsules lying embedded in the 

 parenchyma, such as is found in the genei'a Moudpylidinm and 

 D ' pylidium, was not recognised. The eggs came to be arranged 

 in single layer, spreading laterally from the subcuticular la^'er of 

 one side to that of the other side, and from the anterior iimX of 

 the segment to the transverse vessel. 



The eggs were rounded or elliptical, the outermost shell measur- 

 ing 005 to 0-07 nnn. in diameter, more usually about 0-06 nnn. 

 This shell was thin, delicate, and not resistant. The embryo was 

 elliptical, with a diameter of 0-028-0-039 mm , and invested vevy 

 closely by a delicate shell. This inner shell was in turn sur- 

 rounded by ail irregular l(X)se (albuminous'?) envelope. The 

 embryonal booklets were 0-01 nnn. in length, one half being 

 curved and pointed, the other being straight and obtusely rounded. 



