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W. A. UASWELI.. 
appropriate to the excretory system of the Trematodes and 
the Turbellaria.” 
Perhaps the most remarkable event in the history of the 
development of the excretory system in Temnocephala is the 
change which takes place iu the position of the contractile 
terminal sacs. Originally, as we have seen, they are placed 
close to the epithelium of the endocoele, and apparently open 
into the latter. When the cavity becomes reduced, and the 
pharynx begins to become rounded off, the sacs lose their 
original connections, and, becoming displaced outwards, 
enter into connection with the epidermis, and open on the 
exterior on the dorsal surface. Thus, iu a stage in which the 
rudiments of the tentacles ai’e being formed, the sacs occupy 
the position which they retain in the adult. 
VII. Development of the Alimentary System. 
The alimentary system of Temnocephala consists of two 
principal parts — pharynx and intestine. The mouth, situated 
far forwards on the ventral surface, leads, through a very 
small cavity representing a pharyngeal sac, into the lumen of 
the pharynx. The latter is a large, rounded organ with 
thick walls of highly complex structure. The cavity is lined 
internally by a layer, the nature of which is by no means 
clear. By Weber (18) it has been described as a continua- 
tion of the cuticle of the integument. Mouticelli (14) refei’s 
to it as a syncytial epithelium. Wacke (16) refers to it as 
an epithelium, and gives excellent figures of its minute 
structure. It is a non-cellular layer, in which a degenerate 
nucleus may sometimes be detected, but only quite excep- 
tionally. It is composed of gi’anular material, the granules 
of which are arranged in rows or strings, most, at least in 
the Australasian species, having a vertical direction. Many 
of these strings are traceable in some series into the thick- 
ness of the wall of the pharynx. The internal cuticle, 
described and figured by both Monticelli and Wacke as 
