220 SUMMARY OF CURRENT RESEARCHES RELATING TO 



with the systematic aspect only, the anatomical report being deferred for 

 the present. In his introductory remarks the author insists on the im- 

 portance of distinguishing carefully local varieties, and recommends it as 

 against indiscriminate formation of new si>ecies. About eighty specimens 

 only were collected, which are referable to fifteen genera and thirty species, 

 seven of which are here described for the first time. 



Mouth-lobes of Lamellibranchs.* — Herr J. Thiele has examined the 

 oral lobes in eighteen families of Lamellibranchs, and finds that in many 

 cases they have so characteristic a structure as to be well adapted to be 

 used, with other marks, as distinctive peculiarities. 



They are invested in a single layer of ciliated epithelium, but the cells 

 vary greatly in length ; the long cilia pass through a distinct cuticular fringe. 

 Beneath these there are goblet-cells. "What appear to be sensory cells 

 are to be found in depressions between the ridges, or on elevations of 

 epithelium ; they are always much scattered, and give oif processes into 

 the connective tissue. After describing the difiereuces in these cells in 

 various forms, the author commences his account of the connective tissue 

 with a description of what obtains in Mytihis. Between the mucous cells 

 are branched connective cells which contain " tubes " of intercellular 

 substance ; these are connected with a large blood-space which runs along 

 the upper edge of the oral lobe, and is only shut ofl" from the exterior by 

 epithelium and connective-substance, the latter being not very compact ; 

 this blood-space may be regarded as a true vessel, it is probably arterial 

 and corresponds to the tentacular artery of the Najades. Below the 

 einthelium there is a structureless membrane which, on its inner side, 

 contains considerable muscular and nervous bundles, generally arranged 

 along the long axis of the oral lobe. The fibres which separately traverse 

 the tissue are probably not to be regarded as muscles, but as connective- 

 tissue cells, for the part which surrounds the nucleus often sends off 

 irregular processes, and so marks them as spindle-cells. At the lower 

 margin there are a quantity of cells which Flemming regards as small multi- 

 cellular mucous glands ; the author, however, has not been able to definitely 

 make out efferent ducts. Along the line of fusion of the ridges with the 

 tegumentary fold there are peculiar rods of modified connective substances, 

 which in their relation to the staining reagents correspond to the so-called 

 chitinous rods in the gills. After comparing other forms with Mytilus, 

 the author resumes the results obtained by himself and other authors. 



As to the physiology of these lobes, the first point to attempt to settle 

 was the possibility of their having any function in relation to the ingestion 

 of food. The arrangement of the cilia on the surface beset with ridges 

 on the margin must produce a current which, when the oral lobes do not 

 lie close to one another, must generally direct the firm particles to the 

 margin. Direct experiment with Najades proved the importance of the 

 oral lobes as directive organs. The use of the marginal currents appears 

 to be to drive away the water from which the food has been obtained. The 

 close relation to a large blood-vessel points also to a secondary respiratory 

 function. 



Further investigations are necessary before we can assure ourselves of 

 the justice of Prof. Loven's supposition tliat the labial tentacles of the adult 

 Lamellibranch are the remains of the velum. 



Morphology of Eye of Pectens.t — Prof. 0. Biitschli directs attention 

 to the hitherto unnoticed fact that in the eye of Pecten jacobseiis the thin 



* Zeitschr. f. Wiss. Zool., xliv. (1SS6) pp. 239-72 (2 pis.). 



t Festschrift Naturh.-Med. Ver. Heidelberg, 1886, pp. 175-80 (1 pi.). 



