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PROGRESS OF MICROSCOPICAL SCIENCE. 
" Recent Researches on Kélliker’s Dieyema.—Professor Van Beneden 
has made some very important researches recently on the peculiar 
worms that bear the above name, and which appear to be parasitic on 
the renal (?) organs of various Cephalopods. These researches have 
been fully reported by (we suppose) the. younger Packard in the 
‘American Naturalist. He says that Van Beneden claims of these 
species that they have no general body-cavity. The body is formed 
(1) of a large axial cylindrical or fusiform cell, which extends from 
the anterior extremity of the body, enlarged into a head, to the caudal 
extremity ; (2) of a single row of flat cells forming around the axial 
cell a sort of simple pavement epithelium. All these cells are placed 
in juxtaposition like the constituent elements of a vegetable tissue. 
There is no trace of a homogeneous layer, of connective tissue, of 
muscular fibre, of nervous elements, nor of intercellular substance. 
There is only between the cells a homogeneous substance, as between 
epithelial cells. The axial cell is regarded as homologous with the 
endoderm of the higher animals. He designates as the ectodermic 
layer the cells surrounding the large, single axial cell. There exists 
no trace of a middle layer of cells. We discover no differentiated 
apparatus; all the animal and vegetative functions are accomplished 
by the activity of the ectodermic cells and of the axial cell. On 
account of these characteristics Van Beneden regards these organisms 
as forming the type of a new branch of the animal kingdom which he 
distinguishes as Mesozoa. Hach species of Dicyema comprises two 
sorts of individuals differing externally, one (the Nemuatogene) pro- 
ducing vermiform embryos, the other (Rhombogene) infusoriform 
young. The Nematogenes produce germs which undergo total seg- 
mentation, and assume a gastrula condition. After the closure of the 
blastopore the body elongates, and the worm-like form of the adult is 
finally attained, as they pass through the body-walls of the parent. 
The germs of the Rhombogenes arise endogenously in special cells 
lodged in the axial cell and called “germigenes.’ The germ-like 
cells undergo segmentation, and then form small spheres which 
become infusoriform embryos. The worm-like young is destined to 
be developed and live in the Cephalopod where it has been born, 
while the infusorian-like young probably performs the office of dis- 
seminating the species; it transmits the parasite of one Cephalopod to 
another. This work is also an important contribution to histology, 
particularly to the subject of cell-division. Says Van Beneden, “ the 
recent researches of Auerbach, of Biitschli, of Strasburger, of Hert- 
wich, and those that I have published, have established the fact that 
the division of a cellule, that is to say, the multiplication of the cellular 
individuality, is the resultant of a long series of complex phenomena, 
accomplished in a determinate order, and having their seat as much in 
the nucleus as in the substance of the cell.” Finally, Van Beneden 
places in his branch of Mesozoa the hypothetical Gastreades, which 
