ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 179 



Teredo, Jousseaumiella, and Scioheretia. In Najadae ( Unio ajidiAnodonta), 

 the primordium of the internal gill is not a fold, but consists of papillae 

 arising from in front backwards, and the same method is seen in JVucuIa, 

 Mytilus, Mya, Dreissensia. The fold-method is an abbreviation in the 

 •ontogeny of the branchial system. Wasserloos shows that the reflected 

 lamella of the inner gill arises, not from a plate or membrane, as Lacaze- 

 Duthiers's description suggests, but from a fold. This fold falls into 

 filaments, which form an internal series of filaments, uniting character- 

 istically with the external series. This is true not only in cases of the 

 fold-method of gill-development, bub in at least some cases of the papilla- 

 method. 



Marginal Processes of Lamellibranch Shells.* — Cyril Crossland 

 •enquires into the significance of the ornamental projections which " seem 

 a sad waste of shell-making energy." Their formation is greater in quite 

 young shells than in mature ones of several species. It is great during a 

 period of relative activity, when the young Avicula, Tridacna, or llargariti- 

 Jera is crawling about and seeking a suitable position. Examination of 

 the shell-eating Balistes shows that the smaller and weaker shelled bi- 

 valves are preferred. Moreover, the ornamental processes save their 

 possessors from the attack of Murex ramosus, which kills large numbers 

 of Margaritifera mauritii with small and weak processes, but few of 

 M. margaritifera, which has large, strong processes, which remain well 

 developed to at least six years old. To work its drill the Murex must get 

 a very firm hold with its foot, and the processes make this more difficult. 

 It must be noted that in many cases Murex kills without boring. It 

 breaks a piece of the flexible edge with contractions of its foot ; it pours 

 out the mucus of the foot-glands, which has some poisonous effect ; the 

 bivalve ceases to respond to the stimuli which ordinarily cause a smart 

 closure of the shell. 



Arthropoda. 

 a. Insecta. 



Sense of Direction in Ants.t— F. Santschi has tried to analyse the 

 factors at work when an ant finds its way back to its hill. There is 

 evidence of a chemical and a tactile olfactory sense resident in the 

 antennse. There is also the sense of sight which may assist in some 

 cases, though it is demonstrably unimportant in others. Theoretically, 

 it is also possible that hearing, touch, and a muscular sense might assist. 

 The author has experimented with many diff"erent kinds, e.g. Camponofus 

 maculatus, Messor harhariis, Myrr)iecocystas bicolor, and Aplise nog aster 

 splendida. 



The following conclusions are stated : Two kinds of collecting paths 

 may be distinguished — {a) those based on olfactory and topochemic sensa- 

 tions, especially in agricultural ants, and {b) those based on visual 

 sensations in hunting species. In Tapinoma (and perhaps in other 

 agricultural ants), the path is marked by a literal " scent " intentionally 

 left by a single worker. Even in species that do not carry food to the 



• Proc. Zool. Soc. (1911) pp. 1057 -61 (1 pi. and 2 figs.). 



t Rev. Suisse Zool., xix. (1911) No. 13, pp. 303-38 (6 figs.). 



