658 SUMMARY OF CURRENT RESEARCHES RELATING TO 



while the absence of the ciliated funnels in certain species may be re- 

 garded as a retrogression comparable to what obtains in the renal 

 organs of higher animals. 



A comparison is instituted between the excretory organs of the 

 leeches and of the earthworm, which deserves study, but is not to be 

 ex2)lained without the aid of a number of figm-es. 



Nervous System of Solenophorus.* — H. Griesbach, who is, in a 

 nnmber of points, enabled to confirm the results of Eoboz on Soleno- 

 pliorus megalocejjhalus, describes the ganglia of the scolex as consisting 

 of foiu' ganglia arranged in cruciform fashion, but in two planes ; 

 their substance consists of unipolar and bipolar cells, but the pro- 

 cesses are often altogether absent, and the cells then appear to be 

 rounded ; the ganglia are connected by more or less delicate commis- 

 sm*es, and they give off" peripheral nerve-branches. From the more 

 deeply lying median ganglia a well-developed nerve is given off on 

 each side, which appears to embrace the adjacent sucker. There are 

 signs of these nerves breaking up into fine branches. In the strobila 

 there are two longitudinal nervous trunks, which take their origin 

 from the median ganglia of the scolex, and pass along the margins of 

 the proglottids. The author inclines to the view that we have here 

 to do with an undifierentiated ventral medulla. 



Development of Planaria polychroa.f — E. Metschnikoff was 

 directed to a study of this form in the hojie of being able to find an 

 explanation of the intracellular mode of digestion, and of being able 

 to solve the question as to how far that method is a primitive one. 

 The effort has, however, been vain. 



The author finds that, at an early stage, the embryonic cells enter 

 into so close a relation with the mass of the yolk-cells, that it is for a 

 long time impossible to find any boundary between them ; in certain 

 stages of embryonic development two constituents could be distin- 

 guished ; there were a number of fused yolk-cells, and a much smaller 

 number of embryonic cells which had already become difterentiated 

 into an ejiidermis, a pharynx, and into more indifferent subepidermic 

 cells. Although these are quantitatively more unimportant, they are 

 qualitatively much more important, for the fused yolk-cells serve 

 exclusively as nutrient and suijporting material for the active 

 embryonic cells. 



Each stage in the further development of the embryo is marked 

 by the presence of a large number of yolk-cells within the body of the 

 larva ; during the third day the last remains of the free yolk-cells are 

 absorbed by the larva, which now becomes considerably altered in 

 form. 



Notwithstanding this change of form, these larvas still retain some 

 of their most marked characteristics ; they appear to be radially 

 arranged animals, in which the cortical layer of embryonic cells sur- 

 rounds a considerable mass of yolk-cells. From the third to the fifth 

 day a marked increase is to be observed in the number and size of the 



* Arch. f. Mikr. Anat., xxii. (18S3) pp. 365-8. 



t Zeitschr. f. Wiss. Zool., xxxviii. (1883) pp. 331-5i (3 pis.). 



