ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 493 



5. Lamellibranchiata. 



Frequency of Occurrence of Pearls.* — W. C. M'Intosh directs 

 attention to the irregularity in frequency of occurrence of pearls in 

 mussels, &c. In one lot one in a hundred may contain a marketable 

 pearl, in another lot 50 p.c. may have pearls of a kind, and so on. In 

 700 specimens of Mytilns edulis from the estuary of the Eden, ex- 

 amined by Mr. A. J. R. Russell, pearls were found in 280 of the 620 

 large specimens, and 20 in the 80 small specimens. Thus 42 '8 p.c. 

 had pearls. 



In connection with Dr. Lyster Jameson's view that eider duck and 

 scoter may be the final hosts of the parasites which form the nuclei of 

 the pearls, it is noted that both these birds occur in considerable 

 numbers in the estuary of the Eden and feed on the mussels. It is 

 suggested that some other birds frequenting the mussel-beds, such as 

 the oyster-catcher, may be found to harbour the same parasite. 



Brackish Water Cockles.f — N. Andrusoff finds that the number 

 of distinct genera is greater than has hitherto been recognised. He 

 gives diagnoses and descriptions of Adcena (4 species), Didcma 

 (3 groups), Arcicardium (4 species), Plagiodcena g. n. (5 species), Phylli- 

 cardium, Monodcena (14 species), Limnocardium, Myocardia, Uniocar- 

 dium, Prosodama (17 species), Stytodcena, fforiodcena, and Budmania. 



Arthropoda. 

 a. Insecta. 



Phylogeny of Carabus.J — G-. de Lapouge has made a detailed study of 

 this, dealing especially with Garabus violaceus, the typical form of which 

 is the extreme result of convergent evolution from at least three sources, 

 Iberian, Italian, and Balkan. 



Post-embryonic Development of Intestine. § — P.Deegener has studied 

 this in Gybister roeselii Curtis from the time when the larva leaves the 

 water and begins to pupate in the earth. It is necessary to distinguish 

 (1) the mid-gut epithelium which functions during the last larval stage 

 (apparently without a " Stabchensaum ") ; (2) the " Kryptenhals " cells 

 which are not functional, but form the transition to (3) the crypt-cells 

 or proper regeneration-cells in the fundus of the crypts, structurally and 

 functionally indifferent elements which form the epithelium of the pupal 

 intestine, and along with their descendants the imaginal epithelium also. 



The larval epithelium is separated off and disintegrated ; the 

 Kryptenhals-epithelium is provisional and soon perishes ; it is succeeded 

 by the regeneration-cells which form a pupal epithelium {with " Stabchen- 

 besatz ") ; this again is moulted off and succeeded by a quite new 

 imaginal epithelium. 



Variations of Pieris napi.|| — Ft. Wagner discusses the validity of 

 the sidphurea, sidphureotincta and flavescens varieties of this common 



* Ann. Nat. Hist., xi. (1903) pp. 549-51. 



t Mem. Acad. Imp. Bci. St. Petersbourg, xiii. No. 3 (1903) pp. 1-82 (7 pis. and 

 5 figs.). X Travaux Scientifiques Univ. Eennes, i. (1902) pp. 79-98. 



§ Zool. Anzeig., xxvi. (1903) pp. 547-50. 

 || Verh. Zool.-bot. Ges. Wien, liii. (1903) pp. 174-8 (1 pi.). 



Awj. 19th, 1903 2 k 



