28G ROBERT TRACY JACKSON ON THE 



an area of quiot water within the pipe, in which the fiy could settle and attach them- 

 selves to the smooth glass; (3) the absolute shutting-out of violent currents which would 

 detach them from their precarious abiding places. 



I first found spat on the glass on the 25th of July, 1887, and on the 28th took out a 

 ])ane 6 by 4| inches sqnare on which I have counted eighty-two young oysters, as it is 

 still in my possession intact. This was only exceptional in the size of the glass, as other 

 pieces bore nearly or quite as many spat proportionally to their area. Spat were secured 

 in the pipes until the 29th of October, 1887, when few were left, large numbers having 

 dropped off by the natural dissolving action of the sea-water upon the organic cement 

 by which they are attached. In 1888 the first oysters were found on glass on August 

 1st, and they continued to set into the month of Septenil^ei'. The lateness was probably 

 due to the comparative coldness of the summer. 



Besides oysters, the young of many invertebrates and a\gse attached themselves to 

 the glass, affording admirable opportunities for studying them alive and luidistni-bed. 

 The following attached invertebrates were iwted: 3Iolgida7nanhritknsis,Yem\\; Balanus 

 halcmoides, Stimjison; Serpulas, and other tubicolous worms; Crejndulafornlcata, Lam.; 

 C plana, Say; Ostrea virginiana, Lister., in profusion; Anomia glabra, Verrill, nearly 

 as abundant as the oysters; Pecten irradlans. Lam., attached byabyssus, both very 

 young and quite large individuals, vai-ying from 4 to 1.3 mm. in height; Modiola plica- 

 tala. Lam., attached by a byssus; Argina pexata, Gra^', attached by a byssus; 3Iem- 

 hranip)ora pilosa, Farre, often in lai-ge sheets; Escharella variabilis, Verrill.^ 



The drain-pipes formed a sort of trap, into which many free-moving, crawling, or swim- 

 ming molluscs found their way. "When in the pi[ie they woidd have some dilficulty in 

 getting out, and much valuable material was thus obtained. The following Gasteropods 

 were found entrapped: Scalar ia lineata. Say; Urosalpinx cinerea, Slimpson. This gas- 

 teropod destroys many oysters both young and adults by boi-ing into the shell and 

 killing the animal. I have not seen holes bored by Urosalpinx in Anoniias, though they 

 are quite as exposed as are oysters to its attacks. Littorina litorea, Menke, was found 

 entrapped, both adults and young, in great abundance. Li moving about on the more or 

 less du't-covered glass, this animal makes a trail by the lingual ribbon with Avhich it as- 

 siduously scrapes the glass for its food. The tracks consist of zigzag series of short, 

 parallel lines of cleaned glass, arranged with the longer axes in the direction of the trail. 

 The shoi't lines are almost confluent with the lines of the next succeedino: row; beinjr 

 at first nearly confluent on one side and then on the other, producing a zigzag ])atteru as 

 the animal moves along. Ilyanassa obsoleta, Stimpson, was found in great abundance 

 in the pipes. This species makes a track similar to that of Littorina, but much smaller, 

 as might be supposed from the size of the animal. The differences are that the individ- 

 ual, |)arallel, short lines are less distinctly separable one from another and there is a 

 much larger angle between the successive zigzag series of lines in the track of Ilya- 

 nassa, than is the case with the tiack of Littorina. The last two gastei-opods did good 



' Our sea-anemone, Melridinm mar(iinotum, attaches it- proliably successful method to adopt in stuclying the de- 



self freely to glass slides when in conlinement. The plan velopment of corals T\here very fine results miirlit Ije ob- 



of placing glass in enclosed traps would be a desirable and tained by its employment. 



