380 Transactions of the Society. 



minute points, suggesting their calcareous nature. A moderately 

 decided black cross could be seen, in the tissues of the sac, on 

 rotating the polarizer, and all the spinules polarized. The spicules 

 noticed as doubtful histological elements, clearly belong to calcareous 

 Spongida. 



This very unexpected result of the examination of the specimen, 

 led to the application of the polarizing apparatus to numerous 

 minute portions of the organism which are to be found, here and 

 there, in the Canada balsam around the Carpenteria. These are 

 portions of stolon-tubes and parts of sacs. Some of these have 

 spicules on them, and especially a portion of a large sac within a 

 foraminiferal chamber has a triradiate spicule on it. Now all of 

 these portions and the spicules gave the same results as those just 

 noticed, and it is evident from ordinary microscopic examination that 

 all have the same calcareous structures. Under the employment of 

 a thin quartz plate, the crossed Nicols produce a most splendid play 

 of colours in this little organism. In one specimen which happens 

 to be included within the walls of the Carpenteria there is a tube- 

 stolon and part of two chambers, and the membrane, out of which 

 the spinules stand forth, presents, here and there, the appearance of 

 some thickening at their bases (Fig. 3). 



During an extended examination of this large slide, which 

 contains six specimens of Carpenteria raphidodendron, a body 

 was discovered free in the Canada balsam which is evidently a 

 parent sac of another of the organisms under consideration, and it 

 has its tubes and their developments broken off. 



It is oval in shape, about y^o inch long, and it is less in 

 breadth ; two tubes pass from it from both ends, and they diverge. 

 Under transmitted light the thickness of the body is seen along 

 the track of the stolons which start from the internal membrane. 

 It is greater than that of the specimen already described, but its 

 construction appears to be the same. The spinules are long and 

 very crowded in some parts, especially at the edges, and are in 

 stellate groups on the upper surface. There are the relics of a 

 stolon belonging to another body, on which this very Ascidian-like 

 creature rested. Its spinules polarized light like those of the 

 other forms, but the opacity of the body prevents the coloration of 

 its tissues taking place under the crossed .Nicols except in a very 

 faint manner. 



On examining the dry specimen of the Carpenteria, a portion 

 of one of these bodies was found in one of the chambers, and it 

 was carefully removed. It was dry, brilliantly white in colour, 

 and its elongate sac was covered with minute prickly spinules, and 

 the whole was perfectly opaque. The sac was carefully separated 

 into two portions after being washed in fresh water, which ren- 

 dered it translucent. One portion was mounted in Canada balsam, 



