ANATOMY AND LIFE HISTORY OF MOLLUSCA. 183 



chitinous rods apparently closely united. There is nowhere any 

 aperture large enough to receive one of these eggs, which surround 

 the plume usually in numbers between 200 and 300. 



Siphonaria diemenensis, Q. & G. — The development of the 

 ova in this species is attended with considerable interest, because 

 there is a pulmonary sac in which a gill-plume is contained. I 

 have never observed the ova in the sac, but I have reason to 

 believe that they are developed there. Its position is different 

 from the branchial chamber of the species just described, for the 

 sac is at the middle of the right side, whereas in the genera 

 referred to it is at the back of the head. Into the latter* 

 arrangement the ovary opens, and so it does in the pulmonary 

 chamber, at least I think I have observed such a passage, but 

 this requires further investigation. 



As a rule, in the Gastropods, the ovary discharges into a much 

 looped oviduct, and opens finally into the respiratory cavity. I 

 have been able to examine a newly hatched specimen of the 

 species at the head of this article. The shell was perfectly formed, 

 at least was complete in its conical covering to the foot of the 

 animal. The intestinal tube was partially developed. At the 

 opening which represented the commencement of the mantle 

 cavity around the head, there was a lobe of the mantle studded 

 with from 80 to 90 minute highly refractive round bodies 

 like lenses. At some distance behind this was the Radula 

 already differentiated to its whole extent, and curving round 

 in the position in which it was always found in the adult state. 

 The line of division down the centre was distinct, and the 

 plates with minute teeth passing to each side gradually 

 diminishing in size to the edge. The pulmonary sac and the 

 unformed branchiae could be traced as a series of fine filaments 

 attached to a central rachis. The whole of the mantle was 

 studded with minute hyaline cells of crystalline brilliancy. The 

 liver is distinguished as a mass of brown pigment. The kidney 

 is distinguished as a mass of highly refractive calcareous matter 

 which, with the polariscope, shows curious semi-crystals of yellow 

 and brownish colour. The heart is differentiated and a portion of 

 the aorta can be traced. 



Summary. — The following is an epitome of the facts to which 

 attention is drawn in the preceding essay : — 



1 . Australia is entitled to be considered as a true Molluscan 

 province with peculiar features, and yet not separated in an 

 extraordinary way from Molluscan provinces elsewhere. 



2. The "Australian" characters are more strongly manifested 

 in proportion as the coast-line is followed to the south. 



3. There are few, if any, species common to Australian and 

 European seas. 



