4: 
CHARLES BADHAM. 
Type species A. translucens, mihi. Type specimen' in 
the Australian Museum, Sydney, No. W. 403. 
External Form, 
r The material on which this work is based consists of a large 
number of specimens ranging from the young sexually 
immature to the adult form. From a number of specimens it 
has been possible to arrange a complete series of individuals 
to show the change of form during growth. I would lay 
stress on this very marked change in form, and my observa- 
tions have convinced me of the likelihood of the younger 
forms of similar marine leeches being described as new genera 
or species in the absence of a series of individuals linking up 
the young to the adult. 
In Text-fig. 1 are shown the outlines of specimens which 
measure 1*5, 3, 4, 55, and 7‘5 mm. long, to illustrate the 
change in form which takes place during the growth of this 
leech. Young forms possess a cylindrical body, and the chief 
change in shape during growth is due to the great lateral 
development of the body posterior to the cTitellum. The 
appearance of a specimen 1*5 mm. long is shown in PI. 1, 
fig. 3. When this leech is 4 mm. long the testes become 
mature. At this stage the body is cylindrical (PL 1, fig. 4), 
there is but a faint indication of the clitellum, and the ovaries 
are quite undeveloped. In 6 mm. specimens maturation 
divisions are seen in the ova. At this stage the clitellum has 
become enlarged and is now well marked. 
The young of Austrobdella have the anterior sucker of 
the same diameter as the cylindrical body and the posterior 
sucker nearly twice that size (Pl. 1, fig. 3). When a length 
of 4 mm. is reached the anterior and posterior suckers 
approach one another more closely as regards size and have a 
diameter a little less than the greatest din meter of the body 
(Pl. 1, fig. 4). When the leech has a length of 5*5 mm. 
(Text-fig. 1) the typical form of the adult is foreshadowed. 
At this stage the clitellum becomes evident, and owing to the 
increased lateral development that part of the body posterior 
