20 
ZOOLOGY OF THE FAR EAST. 
them exposed in a shallow dish for 24 hours. They are then transferred to a drop of 
pure glycerine on a slide, and, if there is any danger of crushing, fragments of a 
broken cover- slip are arranged round the drop, A complete cover-slip of relatively 
large size is cleaned and a square or circle of rather thick Canada balsam solution 
painted round it to the requisite thickness. It is then dropped from a pair of forceps 
over the glycerine on the slide, the painted side of course being downwards. The 
glycerine and the balsam are pressed together without mixing. 
It is always as well at the same time to attempt to mount some specimens in 
Canada balsam after clearing them in the ordinary way. Ninety per cent or more of 
such attempts will, in the case of the more delicate tubular species, result in failure; 
but the few zooecia that do not collapse will prove particularly valuable. I am of 
course presuming that abundant material is available, and this is usually the case if 
the investigator be also the collector. 
In the species of Hislopia and Paludicella [i.e. in the most abundant of the true 
freshwater Ctenostomata) there is as a rule no difficulty in clearing preparations with 
oil of cloves, the ectocyst being relatively thick and at the same time more per- 
meable to oils. 
To understand the Ctenostomata and their classification it is necessary above 
all things to study the general anatomy of the polypide and in particular of that part 
of the alimentary canal that lies between the mouth and the stomach. Some confu- 
sion exists in the terminology of this system, more particularly in reference to the 
terms " oesophagus" and "gizzard." The former has been applied in two entirely 
different senses, while the latter has been used indifferently in a morphological and 
in a physiological sense. 
It is in the Division Alcyonellea or Carnosa that the simplest and probably the 
most primitive condition is to be found. 
In Alcyonidium the mouth opens into a comparativelj^ short funnel-shaped 
"oesophagus." The walls of this organ are very thick above and become gradu- 
ally thinner towards its base, which is defined by a circular valve, the so-called 
" cardia" or, as I prefer to call it, the oesophageal valve. When this valve is open 
the lumen of the oesophagus is practically continuous with that of the stomach, 
at any rate when the polypide is expanded. The region that intervenes between 
the valve and the stomach proper or "'pylorus" takes the form of a rather stout 
tube, the walls of which do not differ in essential histological characters from those 
of the latter. There are apparently no circular muscles in the wall of this reg'on, 
which may be known as the cardiac region. 
In the Stolonifera the structure of this part of the alimentary canal seems to be 
essentially the same as in the Alcyonellea, but in the Palulicellea a progressive 
differentiation is found in the different families. In the Paludicellidae (fig. 2, A) the 
only marked changes that occur are that the oesophagus is greatly lengthened and 
more or less distinctly differentiated into an external thick- walled funnel shaped 
"pharynx ' ' and a thin- walled oesophagus proper, and that scattered circular muscle- 
fibres appear in the wall of the cardiac region. 
