Haswett—A Monograph of the Temnocephalee. 101 
is seen that these channels communicate in such a way as to form a network through 
the protoplasm of the epidermal cells. They are frequently dilated into rounded 
spaces, which vary considerably in size under different conditions. In specimens 
fixed with osmic acid, they are never very wide; they are wider in sections of 
specimens fixed with Flemming’s solution and still more dilated in specimens fixed 
with picrosulphuric acid and afterwards subjected to maceration. They are distinct, 
though not large, in sections of specimens fixed with picrosulphuric acid and with 
corrosive sublimate and acetic acid. Those spaces, which are without doubt the 
same as the ‘“ wasser-klare Riiume,” the existence of which in the epidermis of 
the Turbellaria has long been known and frequently been referred to, occur towards 
the outer ends of the canals. Max Schultze’s* and Bohmig’st account of these spaces 
in the Turbellaria would, in fact, very well apply to the case of Temmnocephala. They 
were overlooked by me when I wrote my previous paper on this subject; and to 
Brandes{ is due the credit of first publishing an account of them in 7emnocephala. 
As they are discernible in specimens prepared by so many methods, they are probably 
present in the living condition of the animal; but I am disposed to think that 
whenever they appear of any considerable size in preserved specimens it is owing to 
the action of re-agents. Such spaces are not distinguishable in the living unaltered 
state ; but when a little acetic acid is applied, rounded clear spots soon make their 
appearance and increase in size. A similar effect is produced by pressure—the clear 
spaces by-and-bye increasing till they form blisters projecting on the surface. Max 
Schultze’s account of this phenomenon in the Turbellaria applies word for word to 
Temnocephala—* Wirkt Wasser liingere Zeit auf die Haut eines solchen einem 
ziernlich starken Drucke ausgesetzten Thieres ein, so nehmen die hellen Riiume der 
Haut allmiihig durch Inbibition an Umfang zu, erheben sich iiber die Oberfliiche, 
indem sie die Grundsubstanz vor sich her driingen, und die Cilien auf die Seite 
schieben, werden immer blasser, und platzen endlich um sofort ganz zu verschwinden.”§ 
When acetic acid is seen to produce this effect, it is easy to understand that such 
fixing solutions as contain that or similar acids are likely to cause dilatation to a 
greater or less extent. In 7. guadricornis these spaces appear to be entirely absent 
—the very numerous narrow pore-canals running directly through the epidermis. 
The nuclei of the epidermis are usually spherical or oval, but may be compressed 
in a direction vertical to the surface ; their form appears to vary in a greater or less 
degree with the state of contraction or extension of the body. In 7. mzxor they are 
vertically elongated in the tentacles, flattened elsewhere. They have no definite 
nucleoli, but a closely coiled chromatin filament. In size they differ considerably in 
* « Beitriige zur Naturgeschichte der Turbellarien,” p. 9. 
+ ‘ Untersuchungen iiber Rhabdocéle Turbellarien.” ‘ Zeitschr. f. wiss. Zool.’ LI. (1891). 
+ “* Zum feineren Bau der Trematoden.” ‘ Zeitschr. f. wiss. Zool.’ LII. (1892). 
§ Loc. cit. p. 9. 
