Development (s/'Siphoiiaria austvalii?. 343 



so as to divide it into inhalant and exhalant openings (see 

 fig. 5). 



The experiments of the Kev. J. Tenison- Woods, described 

 in the ' Transactions of tlie Royal Society of Tasmania ' for 

 1876, p. 54, appear to corroborate this view. In the aqua- 

 rium tlie animal always leaves the water, like Littorina ; it 

 would seem therefore to prefer breathing air. 



Nervous System (fig. 6). — The cephalic ganglia are small, 

 and connected by a long and thin commissure ; the optic 

 nerves proceed from them as usual ; but there are no eyes or 

 tentacles. On this point I can confirm Mr. Tenison- Woods, 

 notwithstanding that Quoy and Gaimard have figured the 

 eyes. The pedal ganglia are moderately close ; and each 

 sends off two large nerves to the foot ; otocysts are developed 

 on these ganglia. The parieto- splanchnic ganglia are re- 

 markable for being asymmetrical, both being on the right 

 side ; they send off nerves to the reproductive organs. 



Developvient (figs. 8-12). — The eggs are enclosed in an 

 elongated gelatinous mass attached by one side to rocks, in a 

 more or less semicircular form. The eggs are ovoid, about 

 "007 inch in length, and joined to each other by a fine string. 

 The embryo is at first spherical and ciliated, revolving rapidly 

 in the e,g^^. It then becomes constricted across the middle ; 

 and one of the halves develops stronger cilia, becomes bilobed, 

 and forms a well-developed velum. The other half becomes 

 invested with a nautiloid shell. Two otocysts are developed ; 

 the foot grows out below the velum ; and an operculum is 

 formed on its posterior end. A retractor muscle arises from 

 the periphery of the shell on the left side, and, passing above 

 the body, is inserted in the foot. By means of this muscle 

 the animal can be completely withdrawn into the shell, which 

 is then closed by the operculum. In this state the young 

 animal leaves the egg, and makes its way through the now 

 softened jelly by vigorous use of the velum. Once in the 

 water, the animal swims away rapidly ; and after some time 

 the shell falls off, the operculum still remaining on the foot. 

 The jelly seems to be softened by the attacks of Infusoria. 

 I have not been able to trace the development further. 



These observations were made on ova laid by SipJionaria 

 australis in an aquarium | and there is no doubt as to the 

 species to which they belong. They show that it is a true 

 pulmonate, and that the gill does not indicate an intermediate 

 form between Pulmonata and Branchiata. They also show 

 that the Pulmonata have been derived from oj)erculated bran- 

 chiate moUusks with a curled shell. 



In their reproductive organs and in their dentition the 



24* 



