ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 39 



as the author proposes to call it, D. margaritarum. He suggests that a 

 Sporozoon or the like may also be involved in the death of the Trema- 

 tode ; hut in many cases the Trematode, encysted in August of one year, 

 is liberated from its pearly investment in the following summer. Shortly 

 before liberation the cyst is quite gelatinous. A true or permanent 

 pearl implies the death of the parasite,— is, in short, its " brilliant 

 sarcophagus." 



Origin of Pearls.* — L. G. Seurat calls attention to the observations 

 of Gamer f (1863, &c.) from which it was concluded that pearls in 

 Alasmodon and Mytilus are formed around parasitic Distomes. Even 

 before this (1852) de Filippi had referred to Distoma dwplicatum as the 

 provoking cause. Kiichenmeister (1856) had suggested Atax ypsilophorus. 

 For the pearl oyster, likewise, the importance of parasitic worms in 

 producing pearls has been indicated by Mobius, Kelaart aud Humbert, 

 Thurston, and Giard. But no definitive proof has yet been given, not 

 even by Dubois in his recent paper referred to above. 



Formation and Diseases of Pearls. J — S.Jourdain expounds the view 

 that a lesion, or the presence of an organic or inorganic intrusion which 

 produces a depression of the pallial surface of the shell, is followed by a 

 hyper-secretion of nacreous matter around the nucleus whatever that 

 may be. He alludes to the " nacrotyping : ' which follows when a foreign 

 body is inserted between the mantle and the shell. 



There are two kinds of diseases in pearls, — spontaneous and acquired. 

 In the first case the superficial layers may undergo disintegration and 

 thus destroy " V eclat et V orient de la perle." But, as he has said, this 

 may be doctored. The acquired diseases are due to prolonged and re 

 peated contact with the skin, whose acid secretions, " sebaceous matters 

 and " gaseous emanations " spoil the pearl if their action is long con- 

 tinued. For the pearl so diseased there is no known cure. 



Inferior Backward Current in Bivalve .§ — M. Stenta finds that in 

 " open'' forms (Meleagrina, Anomia), and in those which get rid of sus- 

 pended foreign particles by sudden closure of the shell (Pecten), there 

 is no hint of inferior backward current. In " half-open " forms (Cardium), 

 and in sedentary forms (JSIytilus), there is more or less of an inferior 

 backward current. In Pinna, whose shell lies upright, half-hidden in 

 the sand, there is a strong development of the inferior backward current, 

 and Pinna possesses, in association with this, a special ciliated groove 

 on the mantle. 



Artliropoda. 



a. Insecta. 



Senses of Ants.|| — Adele M. Fielde finds that Stenammafuhum var. 

 piceum apparently follows the trail made by her own feet by means of 

 its scent, but this power of following without hesitation an old track is 

 lost if the tenth segment of the antenna is removed. Similarly, ants of 



* Comptes Kendus, exxxiii. (1901) pp. 700-2. 



t Rep. Brit. Ass. for 1803; Joum. Linn. Soc. (Zool.), xi. (1873) pp. 426-8. 



X Comptes Eendus. exxxiii. (1901) pp. 832-3. 



§ Zool. Anzeig., xxiv. (1901) pp. 521-4. 



|| Proc. Acad. Nat. Sci. Philadelphia, 1901, pp. 521-44 (1 fig.). 



5> 

 J 



