00 XEW GYRODACTYLOID TREMATODES PEOM AUSTRALIAN PISHES, 



ten of which are arranged around the margin of the disc, while the other 

 two are more centrally situated (PI. x., fig. 6). 



The disc has a curiously swollen appeai-ance. In section the swelling is 

 seen to be due to the presence of a mass of peculiar tissue, apparently syncytial 

 in nature, arranged as a number of thick masses vertical to the longitudiaal axis 

 of the animal (PI. ix., flg. 4). This tissue probably acts as a kind of "padding." 



The animal is covered with a thin cuticle which undergoes strong ehitinisation 

 on the disc. Longitudinal and transverse muscle-layers can be distinguished, the 

 former presenting a marked development on either side of the mid-ventral line 

 and assuming the form of two very large muscles passing from the anterior end 

 of the animal backward to become inserted into the hook apparatus of the disc. 

 The posterior portion of these muscles is further strengthened by the addition of 

 another pau-, each member of which passes upward, closely applied to the ovaiy, 

 to become continuous with the longitudinal muscle-layer on the dorsal side. 



The mouth is ventral, but not at the anterior extremity. It leads into a 

 large pharynx which, in turn, opens by a short oesophagus into the intestine. 

 The latter broadens out posteriorly and ends blindly. Into its anterior end, 

 close to the oesophagus, there opens, on either side, a mass of elongated glands. 

 Three pairs of head-organs are also visible at the anterior end, but the corres- 

 ponding glands could not be seen, probably on account of the large mass of yolk 

 surrounding them. No trace of excretory system could be recognised. 



Of the nervous system only the brain was visible. In close connection with 

 this are two pairs of eyes, the anterior being smaller and closer together than 

 the posterior pair. They lie sunk within the body at a distance from the dorsal 

 surface equal to about one-fifthi of the thickness of the animal in this region. 



The testis is a lai-ge triangular organ, situated above and partly behind the 

 ovary, in the mid-dorsal region (PI. ix., fig. 4). The vas deferens is a short, 

 wide, rather irregularly bent tube, opening into the large transversely-placed 

 vesieula seminalis which is connected by a short duct with the cirrus. The 

 latter is a thin, slightly bent tube, lying in a spacious cavity enclosed by the 

 cirrus-sac. The male opening lies mid-ventrally immediately beliind the phai-jTix. 



The ovary is situated slightly anterior to, and below, the testis. The ovi- 

 duct or uterus is a short wide tube opening close behind the male aperture. 

 The shell-gland is only slightly developed, being merely a glandular thickening 

 of the oviduct. There is no vagina. 



The structure of the yolk system is remarkable. There are numerous elon- 

 gated yolk-tubes which converge in two systems and unite to form two trans- 

 verse yolk-ducts, one lying in front of the ovary and testis, the other posterior 

 to them. The anterior system arises by the junction of three minor systems on 

 either side, which bring the yolk from the anterior, middle, and more posterior 

 regions of the body. 



The posterior transverse duct is formed by the junction of a large number 

 of "yolk-tubes" from the lateral body regions, posterior to the anterior system; 

 into this duct there also open a pair of large yolk-ducts (PI. ix., figs. 1, 4) which 

 bring the yolk from the dorsal region of the animal. From the middle of the 

 posterior transverse yolk-duct a longitudinal duct is given off, which passes for- 

 ward beneath the ovary and opens into the ootype. It could not be observed 

 whether the anterior transverse yolk-duet united sepai-ately with the ootj^pe, or 

 whether it and the median longitudinal -yolk-ducts had a common duct leading 

 into the ootype. 



The posterior transveree duct possesses a wide lumen and is very remark- 



