40 SUMMARY OF CURRENT RESEARCHES RELATING TO 



8. Lamellibranchiata- 



Structure of Pearls.* — Fr. Alverdes has studied this in Margaritana, 

 Unio, Mytilus, and Ostrea. He distinguishes between nucleated and 

 non-nucleated pearls. A nucleus is a central body which is not 

 composed of one of the shell-substances. The centre is often a peri- 

 ostracum centre. The pearl-sac is always ectodermic, but its origin 

 remains obscure. The nucleus of a pearl may be a parasite, an ovum, 

 or a fragment of tissue, and some have reported a nucleus made from 

 a quartz fragment or the like. In such cases the ectoderm cells are 

 displaced, and a sort of cyst is formed in which a pearl develops. By 

 introducing ectoderm cells into the mantle parenchyma the author was 

 able to bring about the origin of pearl -sac-like cysts, in which concentric 

 layers of nacre were laid down. 



Epithelium of Anodonta cellensis.f — AY. Siebert gives a detailed 

 account of the minute structure of the epithelium on various parts of 

 the mantle, on the foot, and on the labial palps. The various forms 

 of ciliated, mucus, and sensory cells are dealt with, and the system of 

 currents is mapped out. In an appendix the author discusses the 

 occurrence of lime in the connective-tissue and the wandering cells. 



Arthropoda. 

 a. Insecta. 



Histogenesis of Wing-musculature in Diptera.J— - S. Hansel finds 

 that the whole of the wing-musculature in Pachygaster meromelas arises 

 from indifferent cells lying at the basis of the appendage-disks of the 

 inesothorax. These unite in two nucleated strands crossing one another. 

 The anterior strand forms the longitudinal and the anterior vertical 

 muscles ; the posterior forms the posterior-vertical elevators of the 

 wings. Only unimportant parts of the larval longitudinal and dorso- 

 ventral musculature are utilized. The larval muscle-nuclei probably 

 pass through changes by which, in part at least, they become imaginal 

 nuclei. They thus form a part, though an inconsiderable part, of the 

 imaginal myoblast. The tendons are purely epidermic. The histolysis 

 of the larval musculature occurs by autolysis without any assistance from 

 phagocytes. It appears that the genera] statement may be made, that 

 the wing-musculature in Diptera is always due to two embryonic or post- 

 embryonic dorso-ventral primorclia, with a little help from certain larval 

 muscles. 



Horse-fly of Philippines.§ — M. Bruin Mitzmain has made a study 

 of Tabanus striatum Fabricius, which he finds may aid Stomoxys calcitrans 

 in the transmission of surra {Trypanosoma evansi). The eggs (270-425) 

 are chiefly laid on particles of wood ; the incubation period is 3-5 days; 

 the larvae are essentially aquatic and very cannibalistic ; the larval 

 period lasts for six weeks or more ; there are three distinct moults. 



* Zeitschr. wiss. Zool., cv. (1913) pp. 598-633 (2 pis.). 



t Zeitschr. wiss. Zool., cvi. (1913) pp. 449-526 (39 figs.). 



j Zool. Jahrb., xxxvi. (1913) pp. 465-512 (3 pis. and 18 figs.). 



§ Philippine Journ. Sci., viii. (1913) Sect. B, pp. 197-221, 223-34 (7 pis.). 



