CURRENT LITERATURE. 21 



and illu.strated, giving the memoir especial value as a ^vol•k of reference. 

 The fauna as a wliole is discussed with tlio same thoroughness and the species 

 in detail. An analysis of the data collected leads Dr. Ortmann and Mr. 

 Hatcher to dispute many of the conclusions arrived hy Ameghino and von 

 Ihering. 



The fauna dealt with is regarded as homogeneous, from shallow water, 

 of Pliocene date and Antarctic origin. A comparison of such with similar 

 beds in another hemisphere may he expected to be fruitful of results. The 

 conclusion here adopted is that in late Mesozoic or early Tertiary times, 

 Antarctica enjoyed a milder climate than at present, and extended north to 

 America, Xew Zealand, Australia, and perhaps Africa. Through the warm 

 and shallow seas that washed the Antarctic Continent, or Archipelago, a 

 fauna ranged from Tasmania to Patagonia. 



The Antarctic molluscan fauna entombed at Muddy Creek is the richest, 

 according to the late Professor Tate, known to Paheontology. In compari- 

 son Avith it, the Patagonian fauna is a scanty one. We anticipate that the 

 South American deposits are not yet exhausted. Mr. Hatcher's collection 

 mainly consists of large conspicuous shells, and in all probability, the 

 usual complement of small species, measured by millimetres rather than by 

 inches, yet remain to be discovered. — C. Hedlev. 



Jameson, H. Lyster.— On the Origin of Pearls. Proc. Zool. Soc, 1902, 

 pp. 140-166, pis. xiv-xvii. 



Dr. Jameson has investigated the origin of Pearls in Mytiluti edidis. 

 After a very brief reference to the work of other investigators, he describes 

 the structure of the mantle and shell, and defines the meaning of the terms 

 " pearls," " blisters," and " concretions." As the three terms have been very 

 loosely used in the past, it is important to note that they have each a totally 

 different mode of origin, and should not be confused or regarded as 

 synonyms. A pearl is formed in a closed epithelial sac embedded in the 

 tissues, and formed around a parasite (in Mytiliis a larval Trematode), which 

 probably causes a specific stimulation. It consists of one or more layers of 

 shell-substance, enclosing a central nucleus. Thus there are nacreous pearls, 

 prismatic pearls, periostracum pearls, and hinge pearls. The parasite does 

 not necessarily become the nucleus of the pearl, it may escape before calci- 

 fication, leaving behind a granular substance, which serves as " nucleus " 

 for a pearl. 



Blisters are caused by the intrusion of foreign bodies between the mantle 

 and the shell, or by the secretion of a nacreous cicatrix to close perforations of 

 boring molluscs, worms, &c. 



Concretions are small free calcosphaeritic bodies which occur at times 

 in the connective tissues. In some molluscs they are due to the calcifica- 

 tion of degenerated Sporocysts or of dead Cercariae, and to other causes. 



The author then describes the minute structure, the origin and develop- 

 ment of the pearl and the life-history of the parasite. From Dr. Jameson's 

 work it seems that it is possible to infect Mytilus with the parasite, and he 

 discusses the bearing of the facts in his paper upon the problem of artificially 

 producing pearls. It seems clear from this valuable research, that in many 

 molluscs yielding valuable pearls, Trematodes are one, if not the exclusive, 

 cause of pearl formation. 



