452 M. Vogt on some Inhabitants of the Freshwater Muscles. 
formed of a finely granular substance occur; the globules 
lengthen, become elliptic ; they send out prolongations at one of 
the extremities, at first very broad, which are not distinguishable 
by any peculiarity of their tissue from the body to which they 
are attached. But as they grow, they separate from the body by 
a groove, fill it with granulations, and finally become nearly fili- 
form, coiling themselves up like horns. The body to which 
these appendages belong, grows in proportion, lengthens, takes 
the form of a Distoma, and finally casts off the appendices. This 
separation sometimes takes place under the eye of the observer ; 
and what is especially remarkable is, that the primitive globule, 
which is thus transformed, does not present a cellular structure : 
neither nucleus nor envelope is observable ; it is a simple globule 
of waxy consistence, which is easily flattened by the compressor. 
The Bucephali are, as I have shown by the proportion in which 
they are found, rare in the environs of Giessen. More fre- 
quently, and especially in spring, the sexual organ of the fresh- 
water muscles is found affected by another helminthic dyscrasy. 
The ovary is then coated here and there with small granules of 
a deep red-brown colour. These granules are cysts filled with 
eggs and larve, to which M. Baér has given the name of Dr- 
stoma duplicatum. The body is that of a true Distoma, furnished 
with an appendix still longer than the body, and formed solely 
of large fibres folded in zigzag, and inclosed in a transparent 
sheath. I have found in a single cyst as many as ten larvee coiled 
up, and surrounded by a score of eggs in different stages of deve- 
lopment. The larve and eggs are of a deep orange colour. 
Another guest as yet too little known is met with in summer 
in the viscous liquid surrounding the heart of these freshwater 
muscles: this is the Aspidogaster conchicola of M. Baér. Nearly 
one individual in a hundred is found affected with these curious 
Entozoa. The adult Aspidogasters are almost always filled with 
eggs, in which rolled-up embryos are easily distinguished : what 
most struck me im these embryos furnished with two suckers 
was the detection in them of an organ situated in the first third 
of the body, at the margin of the anterior sucker, closely re- 
sembling the organ of hearing in the larvee of Mollusca. This 
organ is simple, placed on the median lime of the body, and is 
formed of a transparent vesicle, contaming a lithoid body com- 
posed of two rounded and nearly equal halves. The general form 
of the embryos of the Aspzdogaster differs much from that of the 
adults. 
It is evident, from what we have stated, that it is easy to pro- 
cure in the freshwater muscles the necessary materials for the 
investigation of the embryogenic history of a mollusk and of 
three species of Trematoda; but this is not all. 
