F()RA!MlXIl'l':i!.\— IIKHON-ALLEN AND KAltLAXD. 223 



is tlius cruciform in shape, with the angles rounded oft". No external aperture 

 is, as a rule, visible at this stage, but at Station 3 a four-chambered .individual 

 with a slit-like aperture was found. The peripheral walls are rather thick, but 

 are thinner on the flattened faces. In the next stage a fifth chamber is added 

 between two of the chambers of the " cross," and the shell now attains a dis- 

 tmctly rotaline appearance, and has a characteristic rotaline slit-like aperture. 

 Successive chambers are added, at first in a regular spiral (as figured by Merkel) 

 and subsequently irregularly, so as to surround the whole test, which beconies 

 roughly globular with projectmg spherules — like a raspberry (Figs. 4-7) ; and, if 

 this stage of growth continues, tends to become more or less irregular and 

 Gypsina-\ike in form. How long this free stage of existence may continue, in 

 the event of the creature not attaining a congenial host, we cannot say, but 

 some of om- specimens — especially from Ajaccio — are considerably larger than 

 the normal size of the individuals passing into the next, or attached, stage. 



So far as we are aware, no one has yet described or illustrated the actual 

 method of attachment, (^ur large series of N.Z. and Corsican specimens has 

 made this quite clear. The free oi'ganism settles upon some suitable object ; 

 from its under surface it projects protoplasm and forms a thin layer of incrusting 

 chambers connecting it with its host. At this stage (Figs. 8, 9) the method 

 of attachment is not visible round the edges of the young shell, but is easily 

 verified by detaching the individual, or it may be demonstrated in the cases 

 of specimens which have become attached by these delicate connecting chamberlets, 

 and have subsequently broken away again. From these earliest basal chambers 

 the protoplasm then streams out round the spherical embryo, and commences 

 to build an investing wall of chamberlets rising roimd the edges and sides and 

 finally creeping over and enveloping the young individual, as a dome — or nipple 

 shaped — "house" (Figs. 11-18) from which the development of further chambers 

 proceeds, ultimately extending into those branching arms which complete the 

 type (Figs. 19, 21, 22). All stages in this process have been observed in the 

 material at our command. 



It must not be understood from- the foregoing that we regard this as the 

 only, or possilily even the most usual, development of Polytrema. In our material 

 the species occurs literally by millions ; and under such conditions young, free 

 specimens would he expected to occur in similar abmidance, but in point of 

 fact, while in the Corsican material the free stage is extremely common, in 

 the N.Z. material, though a large quantity was very carefully examined, the total 

 number of specimens of this free form was probably under 150. On the other 

 hand, if a series of detached adult individuals is examined, many specimens will 

 be found exhibiting a few central rotaline chambers exposed on the flat base. 

 Our observations of the attachment of the free form show that a layer of small 

 chamberlets is interposed between the " raspberry " stage and the point of 



