4d0 SUMMARY OF CURRENT RESEARCHES RELATING TO 



4. Each sucker receives from tlie ganglion two lateral nerves, 

 each of which corresiionils to a polygonal commissure. 



6. Secoudary ganglia of the inferior commissure give ofl' distinct 

 branches for the suckers. Each sucker is then innervated by four 

 nerves. 



The nervous system of T. elUptica is much simpler, but its study 

 is more difficult from the difficulty of preparing sections. 



The part of the nervous system of T. mediocanellata above the 

 superior polygonal commissure has escaped the author's observa- 

 tion. 



From a histological point of view it is to be noted that the nervous 

 fasciculi traverse the parenchyma without being separated from it by 

 a proper envelope. True ganglionic cells liavo only been found in 

 the scolex. The other nerve-cells differ notably, and possess small 

 oval nuclei. 



Anatomy of the Trematoda.* — The contribution of Herr A. Looss 

 to the anatomy of the Trematoda is based on two new species — 

 Distomum palUatum and D. reticulaium — which were found respec- 

 tively in the bile-ducts of Delphinus deljihis, and under the integument 

 and between the muscles of a shad from Costa Kica. 



The author strongly recommends the adoption of a number of dif- 

 ferent staining reagents; he himself made iise of picro-carmine, alum- 

 carmine, borax-carmine, haematoxylin, and methyl-violet. The value 

 of a number of colours lies in their bringing out differentiations 

 which are never seen when one staining fluid alone is used. 



The body-parenchyma of D. palliatum is extraordinarily thick, 

 and quite prevents any clearing up of the animal as a whole, and it 

 was for this reason that sections had to be resorted to ; the primary 

 mass forms an exceedingly well-developed plexus, the cells of which 

 are of various sizes and have well-marked processes, so that they are 

 closely connected together, and tlie lacunar spaces are proportionately 

 small ; in tliese last there are to be found the remains of the primitive 

 formative- cells, which consist of an, ordinarily, distinct nucleus, 

 around which is a slight amount of protoplasm. In the region of the 

 organs imbedded in the parenchyma the lacunfe of the connective 

 tissue take on a longitudinal direction which runs parallel to the 

 contours of these organs, and so gives the tissue a fibrous api^earance. 



In the investigation of the nervous system, which does not differ 

 in arrangement from that which is ordinarily found in Trematodes, 

 dorso-ventral and surface sections are to be preferred to transverse, 

 for in the last the slight diameter of the nerve-ends causes them to 

 be indistinct and hard to distinguish from the surrounding tissue. 

 The generative organs are of great extent in sexually mature speci- 

 mens ; as in D. hepaticum and some other species, there is a sinus 

 genitalis ; the function of this is discussed, and the conclusion is 

 come to that in Distomes with laterally placed generative pores there 

 is a mode of copulation which may, to put it shortly, be exactly 

 compared to what obtains in snails. 



* Zeitschr. f. WisB. Zool., xli. (1885) pp. liSO-lib (1 pi.). 



