226 SUMMARY OF CURRENT RESEARCHES RELATING TO 



found was three feet ; yet though extremely rough, this was re- 

 travcrsed without difliculty. By what faculty the limpet finds its 

 way back is not yet determined. Eyesight is out of the question 

 owing to the insufficient dcveloi)ment of the eye. In two cases where 

 the tentacles were removed one found its way back speedily, and the 

 other several days after the operation. To destroy any possibility of 

 scenting out the track travci'sed, it was repeatedly washed with sea- 

 water ; but the individual found its way back. The author thinks 

 that the snout plays some i)art in helping the limpet to get home, and 

 that the object of this habit is to avoid being washed oft" the rocks by 

 the tide, they being able to hold on best when fixed to their scars. 



Gill in Neptunea.* — H. L. Osborn describes briefly the develop- 

 ment of Nc])tunca with more special reference to the formation of the 

 gill. 



The head, foot, and vela arise as ectodermal thickenings upon one 

 end of the oval egg ; and soon upon one side, thereby designated as 

 dorsal and oi^posite to the foot, the shell-gland ajipears. This, at 

 first a small ring, increases in size and its rim spreads over the yolk 

 at the end opposite the head, vela, and foot until it has covered half 

 the egg, but the area immediately around the head, vela, and foot is 

 still unencroached upon. This area is in part the region of the future 

 mantle, and just in front of the margin of the shell-area it forms a 

 thickened ridge. This mantle area is now broadly convex as though 

 greatly bulged out upon the dorsal surface of the body. Upon its 

 surface there aj^pears a row of finger-like processes, these being mere 

 folds or thickenings of the surface which form an interrupted ridge 

 running antero-posteriorly upon the dorsal surface of the body. Later 

 this dorsal surface begins to roll inward by an involution which begins 

 near the head, and the mantle cavity is thus formed with the gill, 

 which has been carried along during the involution, lying upon its 

 roof. The formation of a gasteropod gill is here reduced to its 

 simplest terms, namely, a series of dilatations upon the outer surface of 

 the body. This mode of formation is entirely opposed to the conjec- 

 ture of Spengel that the prosobranch gill is as a ctcnidmm which has 

 secondarily become fused with the wall of the mantle cavity. 



The Genus Melibe.f — R. Bergh has an essay on this genus, the 

 representative of an aberrant group of the family of the ^olidise, 

 which, like Tethjs, have undergone retrograde metamorphosis. From 

 Tethjs it is distinguished by the absence of special gills from the 

 base of the pajnllfe and by its much less developed foot, while its 

 pharynx is still provided with the mandibles which are wanting in 

 the Tethyidfe. Nine species have been described. The author selects 

 for special study M. papillosa (de Filippi) from the Japanese seas, of 

 which he has had three specimens. 



Development of the Oyster. J — P. P. C. Hoek, after a full account 

 of previous work upon the subject, details some new facts respecting 

 the development of the oyster. 



* Johns-Hopkins Univ. Circulars, iv. (1884) p. 16. 



t Zeitschr. f. Wiss. Zool., xli. (1884; pp. 142-54 (1 pi.). 



J Tijd. Nederl. Dierk. Ver. Supplemeut Deel i. (1883-4) pp. 2.57-317 (1 pi.). 



