488 
SUMMARY OF CURRENT RESEARCHES RELATING TO 
shaped eyes the sensory cells project at one end into a cup-shaped mass 
of pigment, and at the other are continuous with a nerve-fibril. Such 
eyes are very common, and occur also in Annelid larvas. As in many 
cases simple eyes of these types can only be recognised by the associated 
pigment, it is possible that forms like Arenicola, which are sensitive to 
light but without eyes, may have sensory cells not accompanied by 
pigment. 
N ematohelminth.es. 
Hystrichis and Tropidocerca.* * * § — Dr. 0. von Linstow discusses these 
two genera, whose representatives live in the mucous membrane t)f the 
proventriculus of birds, and almost exclusively in littoral birds. The 
first genus belongs to the Pleuromyaria without lateral ridges, and with 
muscles in the lateral lines, and is also included in Molin’s Acrophalli. 
The second genus, which is one of the Secernentes, is remarkable for 
the extraordinary sexual dimorphism, which is almost unequalled among 
Helminths. 
Giant-Ova of Ascaris.+ — Dr. 0. L. Zur Strassen linds that in Ascaris 
megalocephala the so-called giant-ova always arise from the fusion of two 
separate ova ; thus differing from L. Sala, who held that they might also 
arise from the incomplete division of a primordial ovum. The co- 
alescence may occur at very different stages, and details of the different 
cases are described. If multiple fertilisation occurs, the result is 
abnormal development ; if a single spermatozoon enters, the result is a 
normal embryo of large size. The cells of the germinal area in such 
cases have, like the ova, six chromosomes instead of the typical four. 
Zur Strassen concludes that neither the quantity of protoplasm nor the 
number of chromosomes is of important influence on the development, 
but he lays great emphasis on the number of centrosomes. 
Peculiar Cells in the Cavity of Nematodes.j — Herr W. Schimke- 
witsch describes peculiar elements which he found in the general cavity 
of a free-living Nematode (probably a species of Oncholaimus). They 
occur throughout the whole body, approximately arranged in four rows, 
and sometimes connected with the gut. They are irregular in form, and 
are rich in granules which stain vividly with methylen-blue. Possibly 
they are comparable to the elements of the peritoneal epithelium peculiar 
to Gordiidae, but here remaining in a more primitive unconnected state, 
instead of forming a layer. It is probable that they have some blood- 
purifying function. 
Platyhelminthes. 
Cestodes from Marsupials. § — HerrF. Zschokke has investigated the 
tape-worms taken from a collection of mammals from the Australian 
region. The paper is largely systematic, but contains some general 
statements as to distribution. As far as is at present known, the 
Cestodes infesting Marsupials and Monotremes all belong to the sub- 
family Anoplocephalinae, whose members typically infest herbivorous 
Placentals. There is a certain parallelism between the Cestodes of the 
* Arch. Naturges., lxv. (1899) pp. 155-64 (2 pis.). 
t Arch. Entwickmech., vii. (1899) pp. 642-76 (2 pis.). See Zool. Centralbl., vi. 
(1899) pp. 400-2. % Biol. Centralbl , xix. (1899) pp. 407-10 (2 figs.). 
§ Zeitschr. f. wiss. Zool., lxv. (1899) pp. 392-445 (2 pis ). 
