234 SUMMARY OF CURRENT RESEARCHES RELATING TO 



the brachial groove, and has the form of a flattened funnel, one of 

 whose margins bears cirrhi. The oesophagus forms a curve which 

 rises in front of and above the mouth ; and the latter is therefore 

 further back than the oesophagus which is susjiendcd in a complicated 

 system of lacuna) due to the enlargement of the brachial grooves. 

 The stomach is large, piriform, and possesses towanls its base a 

 constriction to which a membrane is attached. The liver is well 

 defined and more distinct from the stomach than in tlie Brachiopoda 

 artieulata. Tlie intestine bends into a complete ring a little twisted 

 at the side, and terminates in a cylindrical rectum placed obliquely. 

 The rectum is much larger than the intestine and contains at the 

 opening of the latter a sort of valvular fold. The anus is between the 

 two great posterior muscles and traverses a thin membrane stretched 

 between them. The general cavity of the body is divided into two 

 symmetrical halves by a vertical membrane. 



The sexes are separate ; and the genital glands, which arc fully 

 described by the author, are identical in their general disposition and 

 mode of evacuation of the products in the two sexes ; their histological 

 structure alone varies. 



Arthropoda. 

 a. Insecta. 



Compound Vision and the Morphology of the Eye in Insects.* — 

 B. T. Lowne's paper, noticed Vol. III. (1883) p. 64i, is now published 

 in extenso. S. J. Hickson maintains that Mr. Lowne is wrong in 

 denying that the so-called retinuljc are the nerve-end cells of the 

 Arthroj^od eye and correspond with the rods and cones of the verte- 

 brate eye, and he disputes the statements by which Mr. Lowne seeks 

 to prove that all the parts of the eye in front of the basilar mem- 

 brane are dioptric whilst the true retina is situated behind it. Both 

 anatomical and physiological considerations prove the original theory 

 to be true, and morphology also confirms it. In the ocellus of the 

 water-beetle larva the retina is a simple cup of pigmented hypodermic 

 cells in which the optic-nerve fibi'ils may be readily seen to terminate, 

 and these cells are most certainly homologous with the retinula cells 

 of the so-called " compound " Arthropod eye, as shown by Grenacher. 

 Claparede and Weismann's researches on the development of the eye 

 confirm the morphological deductions. 



The " bacilli " of Lowne are connected with nerve fibrils on both 

 sides and thus difi"er from "nerve-end cells" in one of their two 

 fundamental characters. Moreover the bacillar layer is often quite 

 devoid of pigment, no retina purple has been demonstrated and the 

 layer is not always present.! 



"Wings of Hymenoptera.* — An elaborate memoir by E. Adolph 

 deals wdth the morphology of the wings of Ilymenoptera from the 

 point of view of the nervurcs and their relations in diiferent species. 



♦ Nature, xsxi. (1885) pp. 341-2. 



t See also letter in reply by Mr. Lowne in support of his views, and rejoinder 

 by Mr. Hickson, Nature, xxxi. (1885) p. 433. 



X Yurh. K. Lcopold-Curol. Acad., xli. (1884) pp. 61-132 (6 pis.). 



