408 SUMMARY OF CURRENT RESEARCHES RELATING TO 



Larval Eye of Chitons.* — Harold Heath has studied the ocelli m 

 Ischnochiton magdalensis, Trachydermon raymondi, Nidtalina thomasi, 

 etc. As Kowalewsky stated, the eyes of the larva? become clearly 

 defined about the time of the first appearance of the shell ; they are 

 situated immediately behind the velum half-way up the sides of the 

 body ; they are characterised by the pigment deposited about a clear 

 central body. Under no circumstances does the eye of the forms men- 

 tioned become sub-epithelial. In at least eight species they persist as 

 long as the shell and mantle are sufficiently transparent to allow light 

 to penetrate. Histologically they resemble Annelid-trochosphere eyes, 

 and their early development is almost identical. 



Heart of Solenogastres.f — H. F. Nierstrasz finds that the Soleno- 



gastres have a spacious pericardium which may be prolonged distally ; 



that the heart is well-developed, except in Myzomenia and Dondersia, 



and consists of an auricle and a ventricle ; that the auricle arises by 



invagination of the dorsal and ventral walls of the pericardium, or of 



the dorsal wall only ; that the ventricle is always a dorsal invagination. 



There are almost always two auriculo-ventricular openings with 



sphincters. The heart is open dorsally and distally, as follows from its 



mode of origin, but there is a more or less complete closing in by a 



connective-tissue sheath. Ciliated bands, Pruvot's " bourrelets cilies " 



occur on the walls of the pericardium. Except in Myzomenia and 



Dondersia, the heart of Solenogastres, e.g. Neomenia, Proneomenia, etc., 



is by no means a rudimentary organ. Full details of many forms are 



given. 



5. Lamellibranchiata. 



Origin of Tine Pearls. % — L. Boutan has made a study of this 

 subject, and criticises the views of Jamieson and others as to the place 

 of origin of pearls. He is emphatically of opinion that fine pearls are 

 secreted by the external epithelium of the mantle. They have funda- 

 mentally the same origin as the so-called " nacreous pearl " and nacre 

 itself. 



Arthropoda. 

 a. Insecta- 



Gall-Formation. §! — H. Eossig has made many observations and 

 experiments in order to determine what organs in Cynipid larva? stimu- 

 late the formation of galls. He deals at length with the salivary glands, 

 the cenocyte groups of cells, the Malpighian tubules, and the epithelium 

 of the hind-gut. It seems certain that the gall is induced by a chemical 

 stimulus, by a fluid, by a product of the larval metabolism which is 

 exuded very early. It seems clear that the stimulus is not in the 

 vascular fluid, nor in the salivary secretion. Rossig believes that the 

 evidence points to the secretion of the Malpighian tubules, probably with 

 co-operation from the cenocytes. But his results are more conclusive 

 as to what does not cause the stimulus, than as to the actual cause. 



* Proc. Acad. Nat. Sei. Philadelphia, 1904, pp. 257-9 (1 fig.). 



t Verh. K. Akad. Wetenschappen Amsterdam, x. (1903) No. 2, pp. 1-52 (3 pis.), 



% Arch. Zool. Exp., ii. (1904) pp. 47-90 (1 pi.). 



§ Zool. Jahrh. xx. (1904) pp. 19-90 (4 pis.). 



