452 M. Vogt on some Inhabitants of the Freshwater Muscles. 



formed of a finely granular substance occur ; the globules 

 lengthen, become elHptic ; 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 aff'ected 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 larvse, to which M. Baer has given the name of Di- 

 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 larvse coiled 

 up, and surrounded by a score of eggs in difiPerent stages of deve- 

 lopment. The larvse 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. Eaer. 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 in 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 larvse of Mollusca. This 

 organ is simple, placed on the median line of the body, and is 

 formed of a transparent vesicle, containing a lithoid body com- 

 posed of two rounded and nearly equal halves. The general form 

 of the embryos of the Asjndogaster differs much fj-om 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 moUusk and of 

 three species of Trematoda ; but this is not all. 



