Davaineid Cestode from a Wallaby. 605 



tlio usual Davainea type (fi<i;. 2 a), and arc set in two rows, 

 the hooks of the posterior row irrejifiilarly alternating with 

 tliose of the anterior row. They are all of tlie same size, 

 measuring about 9/x long. The crown formed by tliese 

 hooks is very striking, in that they bound an area resembling 

 that of an equal-armed cross, the extremity of each of wliose 

 arms is bitid. Each ray with its subdivisions occupies the 

 middle area of one of the lobes of the protuberance, the four 

 rays meeting on the anterior face of the protuberance. 

 These hooks easily become detached, and cousecpiently it 

 was not possible to determine their number, but a I'ough 

 estimation placed them at about 650 for each row. 



The rest of the head, which is slightly broader than its 

 anterior pi-otubcrance, is separated off from it by a well- 

 defined constriction. 



Tlierc are four rounded suckers placed on slight elevations, 

 each elevation being situated ojiposite one of the depressions 

 in the anterior head protuberance ; thus they occupy a 

 somewhat lateral position, two being subdorsal and two 

 subventral. The outer margin of each sucker is beset with 

 numerous small booklets, about 5 /x long (fig. 2 6), arranged 

 iu diagonal rows of about a dozen hooks in each row. The 

 suckers are somewhat cup-shaped, measuring about 130 yu. 

 across their mouths and having a depth of about 70 /x. 



(c) Neck. — A distinct neck is present, which is of a 

 uniform breadth throughout its length. Its breadth, in 

 different worms, varies from 380 /i to 417 /i, and its length 

 varies from 800 yu. to 1200 /z. This variation a[)pears to be 

 due to the different sizes of the worms, and also to different 

 states of contraction. 



{d) Segments. — The first-formed segments are very short, 

 arid are as broad as the neck, the older segments increase 

 both in length and iu breadth, until about the middle of the 

 strobila is reached, where they are about 230 /a long and 

 4 mm. broad. As the segments become ripe they increase 

 in length and decrease in breadth, so that the ripe segments 

 at the end of the body are about twice as long as broad, 

 measuring about 2"5 mm. in length by 1*3 mm. in breadth. 



Internal Anatomy. 



(a) Muscular System (fig. 3). — The longitudinal muscle- 

 system is well developed, and consists of a single layer of 

 irregularly scattered muscle-fibres occupying the dorsal and 

 ventral thirds of the proi^lottid. The transverse muscle- 

 fibres form a thin layer of delicate fibres immediatelv 

 internal to the longitudinal muscle-fibres; they bound the 



