196 
SUMMARY OF CURRENT RESEARCHES RELATING TO 
are used for things which are by no means homologous. The original 
Olynthus stage was represented by a sac without diverticula ; this 
central cavity, wherever found, should be called the cloaca, and its 
aperture the osculum. In the wall of the cloaca there is a tendency to 
form a special skeleton, and the more it developes the more are there 
definite openings in it, where the diverticula open out ; the term procts 
is applied to the openings of canals or lacunae into the cloaca. In cup- 
shaped Sponges the depression corresponds to the cloaca, and the ulti- 
mate exhalent apertures of e. g. Synops are not oscula but procts. 
The ultimate openings may become complicated as in Cydonium gigas , 
when the excurrent chones do not open simply by one proct, but there 
is a thin covering membrane with a special skeleton and perforated by 
numerous small openings. These openings Dr. Yosmaer calls proctions. 
In the same species the inhalent chones exactly resemble the exhalent, 
and a number of apertures lie together in a membrane (dermal mem- 
brane) over one clione; in this membrane there are small orifices which 
the author proposes to call “ stomions,” and a group of stomions 
corresponds to one stoma. 
Protozoa. 
Infusorian Skin Parasite of Freshwater Fishes.* — Prof. O. Zac- 
charias describes a species of Ichthyoplithirius (J. cryptostomus sp. n.) 
which produces small pits in the skin of Leuciscus rutilus and of Alburnus. 
The infusorian is oval in form, and measures *65- *8 mm. in length 
by *5 mm. in breadth, large enough to be mistaken for a Turbellarian. 
There is a large horseshoe-shaped nucleus. Cilia cover the surface ; the 
endoplasm contains refractive grains and small crystals and is vacuolar 
though without contractile vacuoles. No micro-nucleus was detected, 
nor a distinct mouth, but there is a small pit, which may be a fixing 
organ, on the ventral surface. As to reproduction, the parasite becomes 
encysted, divides into two, and by rapid further divisions into 100-150 
young forms which have a macro- and a micro-nucleus. Not only does 
the parasite injure the fish by loosening the epidermis, but it prepares 
the way for Saprolegnia ferox or other fungi. A similar parasite was 
described in 1876 by D. Floquet under the name Ichthyoplithirius 
multifillis. 
Flagellata.l — Dr. G. Klebs has made a detailed study of Flagel- 
lata, in fact his memoir may be called a provisional monograph. He 
begins by pointing out that although there are distinct types of Protozoa, 
there are no rigid boundaries between the different classes. Most 
Flagellata divide longitudinally, but Oxyrrhis marina divides trans- 
versely, and it is likely that other exceptions to what seemed not long 
ago to be a general rule, will be discovered. Klebs enters into a detailed 
discussion showing that the Volvocinese must be kept apart from Flagel- 
lata ; the differences in life-history and reproduction are great. The 
periplast or external plasmic layer, so characteristic of Flagellates, and 
the entirely different secondary envelope ( Hiille ), are then described 
at some length. The following definition is proposed : — 
* Biol. Centralbl., xiii. (1893) pp. 23-5. 
f Zcitschr. f. Wiss. Zool., lv. (1892) pp. 265-445 (6 pis.). 
