354 8UM11A.RY OF CURRENT RESEARCHES RELATING TO 



elusions. Much of what is of value in his history of the vascular 

 system will be found to be due to his recognition of the fact that, in 

 this question, there is a limit to niacroscopical inquiries, and that the 

 assistance of the Microscope is necessary. He has thus been able to 

 make out the great size of the so-called capillary tubes. By the aid 

 of experiment ho was able to deprive the heart of the greater part of 

 its blood, and to force on himself the question, whither has that blood 

 gone ? and in this to convince himself of the presence of haemal spaces 

 in the gelatinoiis tissue. 



The blood in the lacunar system would appear to be gradually 

 collected from the most various parts of the body by venous vessels ; 

 from the lacunte of the foot and of the anterior portion of the mantle, 

 it passes into the truncus venosus, which lies below the rectum, and 

 opens into the pericardium. The veins are true vessels, with a lining 

 of endothelium, but they are not so highly differentiated as is the 

 arterial portion. Although there can be no doubt that the vascular 

 system of Laraellibranchs is, in all its parts, capable of enormous ex- 

 tension, there does not appear to be any sufficient ground for believing 

 that there is a special tissue at the points where this extension more 

 particularly takes place. For this we must look especially to the 

 presence of lacunar spaces. As to the arrangement of these last, it 

 does not seem possible at present to arrive at any generalizations. 

 The author points out the differences between true capillaries and 

 such lacuufB as those which he describes. 



A suitable object for the study of the ingestion is afforded by 

 Ci/clas cornea, examined by low power, when placed in a watch-glass. 

 The cilia will be found to be in active movement, working at the 

 respiratory cavity from without inwards, and in a reverse direction at 

 the cloacal orifice. Experiments with carmine will, if rapidly per- 

 formed, make this still more obvious. The author enters into an 

 account of the best way of observing the phenomena, and of the 

 special experiments which he undert(jok. 



The Naiadfe have three pon aquiferi in the foot, and by these the 

 water passes directly into the blood ; the slit-like pores in Mylilus and 

 Dryssena lead into a canal-like duct, which is wider in the former 

 than in the latter ; in both we find a ciliated cylindrical epithelium 

 surrounding the pore. The duct ajjpears to be nothing more than a 

 lacuna, with which a number of vascular-like lacunas are connected, 

 and the whole water-tube is traversed by numerous muscular fibrils, 

 to the presence of which the vascular appearance of the lacunfe may 

 be ascribed. The author believes that this ingestion of water is a true 

 part of the respiratory activity of the Lamellibranchs, and he thinks 

 that, of necessity, the action must be a constant or permanent one. 



Generative Organs of the Oyster.* — After an elaborate biblio- 

 graphical account, P. P. C. Hoek investigates the structure of these 

 organs in detail. 



He finds that the reproductive organ of the oyster consists of the 

 genital gland, and its efferent ducts, without any accessory organs. 



* Tijclschr. Nederl. Dierk. Ver., Suppl. i. 1 (188?.) 253 pp. (1 p].). 



