942 SUMMARY OF OURBENT EESEAROHES RELATING TO 



relation to the mantle, but is placed quite beneath the foot, and surrounds 

 the operculum, as to the pedal nature of which there is no doubt. 



Byssus Gland of Lamellibranchs.* — Herr L. Eeichel is of opinion that 

 the byssus of Lamellibranchs is a cuticular structure, the roots of which are 

 formed in the byssus-cavity, and the filaments in the groove of the foot. The 

 glandular cells which should be present, were the secretion-theory correct, 

 are never to be found. The groove can, by the approximation of its edges, 

 be converted into a complete canal, the lumen of which is semilunar in 

 shape. The epithelium of the canal and of the cleft continuous with it 

 are distinguished by two characters : in the latter the cilia are placed on a 

 cell-membrane, which, in cross-section, has a distinctly double contour ; in 

 the former there is but a single line between the byssus-substance and the 

 epithelial cells ; each cell of the canal has only one process, while those of 

 the cleft have each several cilia. Other objections are raised to the 

 secretion-theory. 



New Sensory Organ in Lamellibranchiata.f — Dr. J. Thiele has 

 examined the two yellow papillae found near the anal papillae in Area 

 Nose. He finds that they are closely covered by long immobile hairs, and 

 that in transverse sections their epithelium has a striking resemblance to 

 that of the lateral organ of the abdomen, described by Eisig in the 

 Capitellidse. Internally there is a considerable layer of granules, among 

 which is a network of processes, and thin spindles and rods. The author 

 proposes to call these bodies abdominal sensory organs. They are 

 supplied by a nerve which branches off from the most median of the nerves 

 which extend backwards from the visceral ganglia ; beneath the organ 

 is a small ganglion, whence the separate nerve-fibres pass to the sensory 

 cells. 



Similar sensory spheres have been found not only in the closely allied 

 Pectunculus, but in Aviculidse, Pectinidas, and Ostrseidge ; they are dis- 

 tinguished fro mEisig's organs by their want of retractility, but this may 

 be explained by their protected position in the mantle space. The author 

 has not yet been able to find these organs in siphoniate Lamellibranchs, but 

 the specimens examined were not very satisfactorily preserved. 



/« 

 Molluscoida. 



a. Tunicata. 



Observations on Ascidians. J — Miss L. Sheldon commences with a note 

 on the ciliated pit of Ascidians in its relation to the nerve-ganglion and 

 so-called hypophysial gland. In the adult forms examined four main 

 variations of the pit were observed ; in ClavelUna it is simple in shape, its 

 opening into the mouth being round in section ; it is situated ventrally to 

 the nerve-ganglion into which it leads by a wide opening ; in Amaroecium 

 the pit is shorter and simpler, and has no connection with the ganglion ; 

 the mass of spongy tissue into which it opens appears to be degenerated, 

 and somewhat resembles the notochordal tissue of vertebrate embryos. In 

 Ascidia and Ciona the pit consists of a ciliated funnel passing into a canal ; 

 and in Phallusia mammillata there is a large reservoir lying ventrally to 

 the ganglion which communicates with the mouth, by a comparatively 

 small orifice. 



In the embryo oiAmaroecmm the nervous system consists of four portions ; 

 an anterior dorsal part which exactly resembles in structure the ganglion 



* Zool. Aiizeig., X. (1887) pp. 489-90. t Ibid., pp. 413-4. 



X Quart. Journ. Micr. Sci., xxviii. (1887) pp. 131-48 (2 pis.). 



