ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 161 



for water to be forcibly ejected from the shell in swimming without 

 injming the gills. The large size of the animal (7 inches in length) 

 makes it possible to inject the vascular system successfully. The visceral 

 ganglia are very large and complicated. The circumpallial nerves and 

 the branchial nerves have ganglion-cells throughout their length. The 

 otocyst canals open on the surface of the body. But we cannot do more 

 than select a few points from this careful study. 



Hinge of Jltheria.* — L. Waagen has made a detailed study of the 

 remarkalile, much reduced, and partly obliterated hinge (of the Najad 

 type) in ^theria, correlating its peculiarities with the attachment and 

 inward shunting of the ligament-complex, and discussing its taxonomic 

 interest. He has also notes on a tyjje of a new sub-genus — Glessinella 

 sturanyi. 



Arthropoda. 



a. Insecta. 



Evolution of Social Bees.j — R. Dittrich notes that the gulf between 

 solitary and social bees is not so real as used to be supposed. Tran- 

 sitional states are now known. It has been pointed out by von Buttel- 

 Reepen that the social mode of life is marked by three distinctive 

 features : — (1) the differentiation into fertile females and workers ; (2) the 

 utilisation of wax for some kind of comb ; and (8) the accumulation of 

 stores, especially of pollen and nectar. As regards modes of life, the 

 following series may be suggested. 

 I. Bees living alone : 



A. The mother dies after oviposition and providing food for the 



larva3, but without ever seeing the brood. 



1. The nests are formed quite apart : Frosopis, Oeratina, 



Osmia papaveris, etc. 



2. The females work independently, but the nests are 



formed in colonies, and there may be mutual aid 

 against attack : Anihreiia, Anthophora, Chalicodoma, 

 Osmia, etc. 



3. Females, or females and males, hibernate in companies : 



Halictus morio, XijJocojja. 



4. Two or more females use a common hole of refuge : 



Panurgas, Halictus, etc. 



B. The mother survives to see the brood and watches over the nest. 



5. Halictus sexcinctus. 



6. The cells form a comb : Halictus quadricinctus. 



7. The first-born young are all females, they work in the 



old nest, and parthenogenetically produce males and 

 females : Halictus scahiosus. 



8. The next stage (according to Buttel-Reepen) should be 



that in which the mother and the parthenogenetically 

 reproductive young work together in the old nest ; 

 but a representative of this stage has not yet been 

 found. 



* SB. k. Akad. Wiss. Wien, cxiv. (1905) pp. 153-82 (1 pi. and 2 figs.). 

 t Jahresb. Schlesischen Ges. vaterland. Cultur., Ixxxiii. (1906) 2te Abt. (Zool. 

 Bot. Sektion) pp. 1-2. 



ApriJ 17 th, 1907 M 



