"WOODWARD: ANATOMY OF MULLERIA DALTI. 91 



In conclusion, on this point we may safely state that the similar 

 condition of the heart observed in Ostrea and Mulleria has been 

 brought about by the action of similar causes possibly induced by 

 a similar habitus, it being an example of what is known as con- 

 vergence, and having no phylogenetic significance. 



The Kidney or Organ of Bojanus. — The kidney calls for no special 

 comment; it is essentially that of a typical Eulamellibranch, and 

 closely resembles that of Anodonta in every detail. 



The Genital Organs. — A large genital duct {g.a.) opens close to, but 

 perfectly independent of, the external opening of the kidney in the 

 supra-branchial chamber. The genital gland is extensive ; it surrounds 

 the coils of the intestine, and even extends round the rectum above 

 the pericardium. 



The Alimentary Canal. — The mouth practically leads direct into the 

 stomach, an oesophagus, as such, not being present. The digestive 

 glands are situated below and at the sides of the stomach, into which 

 they open. There is no crystalline style or ' fleche tricuspid.' The 

 intestine is fairly long and bent on itself several times : before leaving 

 the visceral mass it enlarges abruptly ; this point evidently represents 

 the junction of the mid-gut with the hind-gut. The latter passes 

 dorsally and continues to enlarge, becoming considerably dilated just 

 in front of the heart ; from this j)oint it runs posteriorly, and gradually 

 diminishes in size, finally opening into the supra-branchial chamber 

 above the adductor muscle. The hind-gut is characterized by the 

 possession of a longitudinal infolding of its ventral wall, forming what 

 is known as a typhlosole {t.). 



The Nervous System. — The only point of interest connected with 

 the nerves is the presence of well-developed pedal ganglia ; this, in 

 face of the entire suppression of the foot, suggests that the latter 

 has only recently been aborted. The cerebro-pedal commissures are, 

 however, somewhat short. Owing to the great transverse width of 

 the mouth, the cerebral ganglia are widely separated, and their trans- 

 verse connective is consequently long. 



Conclusions. — In the structure of its gills, of its kidney, and in the 

 relationships of the urinary and genital ducts, Mulleria is a typical 

 Eulamellibranch, but owing to its specialized mode of life it has 

 undergone several striking changes. With the loss of locomotion the 

 foot has atrophied, and apparently also in connection with the fixed 

 habit the anterior adductor muscle, present in the young, has dis- 

 appeared, and the posterior enlarged. This enlargement has brought 

 about that Ostrean character, the separation of the heart from the 

 rectum. 



In its general organization, and especially in the details of the 

 gills, the mantle lobes, and the kidney, Mulleria approximates to the 

 Unionidse ; and the conclusion which I should arrive at from a study 

 of the soft parts of this mollusc would be in entire accord with those 

 already advanced by conchologists from a study of the shell, viz. : 

 that Mulleria is closely related to the TJnionidse, but is extremely 

 specialized in accordance with the fixed mode of life which it has 

 adopted. 



