M. Vogt on some Inhabitants of the Freshwater Muscles. 451 



of perfect individuals, frequently swarm in the organs of these 

 animals. During my stay at Giessen I undertook a series of 

 researches on the embryology of the various animals which in- 

 habit the freshwater muscles ; these investigations were inter- 

 rupted by the revolution of 1848. Having no opportunity of 

 resuming them immediately, I consider it a duty to call the 

 attention of naturalists to a field of investigation which promises 

 a rich harvest. Embryologists especially will find in the fresL- 

 water muscles matter to satisfy them ; for they present not only 

 their own eggs and the larvae of bivalves which hatch in their 

 gills, but also eggs and embryos of Entozoa, of articulated and 

 even vertebrated animals. 



The eggs of the freshwater muscles pass into the gills in the 

 beginning of May. I have not been able to observe the passage 

 itself, but I have notwithstanding traced the development of the 

 e^^ in the first stages of the embryogenic process. I have seen 

 the division of the vitellus in all its phases, up to the formation 

 of a globular embryo, which still wanted a shell. By comparing 

 the eggs concealed in different parts of the gills, I convinced 

 myself that the eggs placed near the anus were more advanced 

 in this process than those which were in the anterior portion 

 of the gills; the latter therefore appear to be filled from be- 

 fore backwards. The eggs, in the ovary, arrived at a certain 

 stage of maturity, are always composed of a transparent envelope, 

 and of a granular vitellus of a whitish, yellow or orange colour, 

 in which is situated the Purkinjean vesicle. This vesicle is very 

 large, entirely transparent, and always contains two small vesi- 

 cles (germinative spots of Wagner), one of which sometimes pre- 

 sents a granular appearance. It is a general law, as regards the 

 eggs of the Unios and Anodonts, that these spots are to the num- 

 ber of two in each e^^. 



The ovary and testicle are the habitual seat of those larvae of 

 Trematoda, which M. Baer has designated under the name of 

 Bucephalus polymorphus . The figures which M. Baer has given 

 of these singular animals are tolerably correct. They are formed 

 of a distomoid body placed on two long rolled-up appendices 

 which have a serpentine movement. These larvae are developed 

 in the long filiform intestines, which, under the microscope, ex- 

 hibit now and then swellings, in which are lodged the Bucephali. 

 The sexual organ affected by this dyscrasy resembles a mass of 

 entangled white threads ; 1 found one individual in about two 

 hundred freshwater muscles, the ovary of which had the appear- 

 ance of a fibrous schirrus macerated for some time. These threads 

 are especially developed in January and February ; and it is also 

 in these months that the development of the Bucephali may be 

 easily observed. In the swellings of the intestines, 2:lobules 



29* 



