440 ANATOMY OF THE LAMELLIBRANCHIATA. 



a triangular process, situated between the muscle and the 

 branchiae. This last is the part we see alone developed in 

 the Pecten and Spondylus. When the foot is large, the ova 

 are contained in it, and do not extend into the other parts. — 

 The orifices of the short oviducts vary in situation, but are 

 always in connection with the excretory organs, as has been 

 mentioned above. In the oyster, according to Home, they 

 open under the mouth, * but in the Anomia they open farther 

 back, between the branchiae. In Cardium, Solen, Pholas, 

 Psammobia, Mactra, Venus, Venerupis, My a and many 

 others, they open by papillae at the posterior part of the foot 

 into the excretory organs. In Unio, Modiola, Mytilus, Li- 

 thodomns, Hiafella, and some others perhaps, the orifices of 

 the eviducts do not open into these organs, and are more or 

 less distant from their outlets. The ratio of these differences 

 appears to be the situation of the ovaries. The ovaries are 

 scarcely visible at some periods : when developed, they often 

 present an agreeable arborescent appearance. The animals, 

 in such a state, are considered in season as articles of food. z 

 The ova leave the oviducts at different periods of the year in 

 different species ; this however generally takes place in spring 

 or at the commencement of summer. Poli asserts that some 

 species discharge their ova more than once in the year. The 

 ova are contained in the ovaria, enveloped by membranes, 

 each of which contains several. At an uncertain time before 

 their discharge, a milky fluid makes its appearance in the ova- 

 ries, and is itself ejected from the oviducts some time before 

 the ejection of the ova. When this fluid, which is often of a 

 light pink colour, is examined with a lens, it is seen to con- 

 sist of minute oval bodies, not more, perhaps, than the four 

 thousandth part of an inch long, swimming in a fluid, and 

 having a very perceptible motion. With a lens of upwards 

 of the twentieth of an inch focus, these appear simply oval 

 bodies, without appendages of any sort. Minute species of 

 Vibrio abound in this fluid, and these, becoming entangled 

 with the oval bodies, sometimes give the latter the appear- 

 ance of having appendages. 3 Before the appearance of this 



1 Home, Croonian Lecture. 



2 It is extraordinary that muscles should have a poisonous effect on some 

 persons at certain times, whilst occasionally they may eat them with impu- 

 nity ; and other persons will partake of the muscles which appear so perni- 

 cious in certain states of the system, without any bad effects. It appears 

 to be quite unknown to what this pernicious property may be owing ; it has 

 Q&en caused death. See Orfila, Moehring, Rondeau, Burrows, and Fodere. 



3 Though the author calls in question the facts recorded by such observ- 

 ers as MM. Prevost and Dumas, with considerable hesitation, he is inclin- 

 ed to think, with M. Raspail, that they have mistaken the vibratile parts of 

 other organs for seminal animalcules in these animals. 



