116 



by Mr. J. V. Thompson in the fourth Memoir of liis <Zoological 

 Researches.' The young of Balanus is there described as being, 

 vvhen -^Ūi of an inch in length,a free swimming animal, resembling 

 Cyclops in its general form, and baving pedunculated eyes: and itis 

 stated that itthen throws oflPits bivaive-shell-like envelope togetber 

 vvith the greater part of the black colouring matter of the eyes, be- 

 comes fixed and covered vvith calcareous matter, and is changed 

 into a young Barnacle, such as is described by Pennant as Balatius 

 pusillus, the arms at the šame tinie acquiring the usual ciliated ap- 

 pearance. In Mr. Gray's specimens of the young, on the contrary, 

 the general form of the adult is fonnd, and the arms are ciliated 

 while it is still in the egg, its totai length being less than -j^th of an 

 inch. Of this length it is also by no means uncommon to find 

 common Barnacles attached. 



Mr. Gray added that on examining the eggs vvhich are found 

 around the base of the animals of Penlalasmis, Leach, and Otion, 

 Ej., he had observed indications of the existence of young siniihir 

 to the adult. They were not, however, sufiRciently developed to 

 cnable him to describe them vvith precision. 



Mr. Gray also called the attention of the Society to a fact con- 

 nected vvith the history of some of the marine Gasteropodous Mol- 

 lusca, vvhich he had observed on the šame occasion vvith the young 

 of the Bąlant. It is well knovvn that the animals of terrestrial shells 

 are torpid during the vvinter in cold and temperate climates, and 

 during the dry season or summer in tropical regions ; but it had not 

 been previously remarked that a simiiar statė occurs in those of 

 marine shells. Mr. Gray found that many individuals of Littorina 

 petrcea, and some of Litt. rudis, were in this condition during his 

 stay at Davvlish. They vvere attached to the rocks several feet 

 above the reach of the highest autumnal tides; their foot vvas en- 

 tirely retracted ; and a membranous film vvas spread betvveen the 

 rock and the edge of the outer lip of the shell : the gills vvere only 

 moist, the branchial sac being destitute of that considerable quan- 

 tity of vvater vvhich exists in it in those of the šame species vvhich 

 are adherent to the rock by their expanded foot. In this torpid 

 condition, the individuals observed by Mr. Gray continued during 

 the vvhole of his stay, vvhich lasted for more than a vveek. On re- 

 moving several of them and placing them in sea vvater, they re- 

 covered in a ievf minutes their full activity. 



Mr. Gray further stated that he had on the šame occasion ob- 

 served that the animal of Rissoa ■parva has the povver of emitting 

 a glutinous thread, by vvhich it attaches itself to floalingsea-vveeds, 

 and is enabled, vvhen displaced, to recover its previous position. A 

 simiiar property, he remarked, vvas Jongsince observed in one ofthe 

 land Mollusca, a species of Limax, Linn. ; and it Iias recently been 

 recorded by M. Sander Rang as occurring in a marine genus of 

 Mollusca, to vvhich he has given the name of Litiopa. Mr. Gray 

 added his belief that it vvould probably be found to be common to 

 many species of marine Mollusca. 



