56 RECORD OF CURRENT RESEARCHES RELATING TO 



The authors say that the gustatory papillae of the Pterotrachea 

 have the same structure as those of the Mammalia. The internal 

 cone is surrounded outside by sensitive cells with a large vesicular 

 nucleus, occupying the greater part of their body. These are 

 connected with nervous fibrillse, and have on the peripheral extremity 

 a long sensitive hair. The sensitive hairs of the gustatory cells of 

 the oral papillse traverse the canal of the cuticular layer, and reach 

 the level of the gustatory pore ; whereas in the organs of the external 

 skin, where the cuticular layer is thin, the sensitive hairs start 

 from the gustatory pore and rise above the surface in the form of a 

 brush. 



Each sensitive organ receives a nervous fibre, which is much more 

 apparent in the organs of the external skin, and it is here clearly seen 

 how a nervous fibre separates from the main nerve to each organ, 

 passing through the cartilaginous layer to the base of the papilla. 



The nerve of the Pterotrachea possesses a transparent elastic 

 sheath and an axis- cylinder which is clearly seen to be formed of 

 fibrillje. When the nerve reaches the base of the gustatory organ it 

 is without a sheath, and the fibrillse of the axis-cylinder separate, 

 penetrating into the gustatory corpuscles, and join with the central 

 extremity of the gustatory cell. 



The authors promise to extend their investigations to other species 

 of Heteropoda. 



Development of the Chitons.* — All the forms examined by Pro- 

 fessor Kowalewsky were moncecious, and the males were observed to 

 emit their sperm through two orifices, which are placed superiorly to the 

 branchiae. The females laid their eggs somewhat later, and, in many 

 cases, during the night ; they were similarly passed out fi'om two supra- 

 branchial orifices, and seemed for a time to remain attached to the 

 gills, where they were fertilized by the spermatozoa contained in the 

 stream of water which passed over these organs. In Cliiton Polii 

 the ova passed through their early stages of development before 

 leaving the protection afforded them by the gills ; in some species 

 the investing chorion became impregnated with calcic carbonate. 



Cleavage is regular, but after the appearance of the sixty -fourth blas- 

 tomere the sphere becomes divided into two halves, and the cells in the 

 upper divide more rapidly than those in the lower region ; this gives 

 rise to a stage in which the embryo forms a somewhat elongated 

 sphere and contains a small blastoccele. The gastrula now begins to 

 be formed in the following fashion : the lower and median portions of the 

 half which contains the larger cells begin to be invaginated ; a ring, 

 formed of two rows of cells, is formed around the egg, and divides it 

 into a superior (cephalic) hemisphere, and an inferior (invagination) 

 hemisphere ; the cells of the latter, which are much the largest, deve- 

 lop cilia, and on the half of the embryo which lies opposite to the 

 invagination orifice there is differentiated a group of three or four 

 cells, which, by developing cilia, form the anterior tuft. The gastrula 

 has now the form of a body in which the blastopore is placed at the 

 inferior pole, and in which there is a double row of ciliated cells, 

 * 'Zool. Anzeiger,' ii. (1870) p. 469. 



