560 Transactions of the Society. 



Descri'ption of the Spicula. 



One of the most striking examples of the symmetrical en- 

 largements of parts of an axial canal, is seen in a well-preserved 

 spicula of the " acuate, hasally rectangulated " type of Bowerbank 

 (Fig. 1). The spicule is rh^ inch long and tt)Vo inch broad 

 at its thickest part, and as its name implies, it is walking-stick in 

 shape, rounded at the base, and acuate-attenuate at the other end. 

 The curve of the basal end is at right angles to the stem, which is 

 broadest just below the junction of the handle. There are eight 

 enlargements of the axial canal, which, where perfect, is about yV 

 of the diameter of the spicule. The first, at the basal end, is 

 a globular swelling ending in a simple enlargement of the axial 

 canal ; the second is at the junction of the handle and stem, and is 

 a long and wide space, increasing gradually in breadth to a certain 

 point, and then diminishing suddenly to the normal dimension of 

 the axial canal. Then follows a short normal canal, which 

 suddenly enlarges and again very gradually diminishes, to its 

 original calibre. This third enlargement is much smaller than the 

 first, and the shape is the reverse of the larger one. A very short 

 piece of axial canal follows, and it again enlarges for the fourth 

 time in a manner similar to that observed in the third enlargement, 

 but to a greater extent. A fifth and broader enlargement succeeds, 

 with barely any intervening normal axial canal, and it is well 

 rounded in front and angular towards the end of the spicule. 

 Three others succeed, and they are small, but of the same general 

 shape. The last ends in a normal canal which opens externally, 

 and has not its termination within the spicule. 



The shape of the enlargements — elongated tear-shaped — is very 

 remarkable, and they differ amongst themselves only in length and 

 breadth. The second enlargement occupies at least one-half of the 

 width of the spicule, and the fifth quite three-quarters of it ; so 

 that there is little solid matter left around. This very remarkable 

 spicule has the enlargements of its axial canal filled with the 

 balsam in which it is mounted. 



Now, a second specimen of the same type, has the axial canal 

 inflated and swollen here and there, but the enlargements do not 

 resemble those of the spicule just described in size, shape, or 

 position (Fig. la). 



A third specimen of the same shape, has the whole axial canal 

 enlarged about three times its normal width ; and a fourth specimen 

 is quite normal, having an excessively delicate axial canal without 

 any swellings, and being minute and tubular. The length of 

 these spicula is about tJ^j- inch, and the greatest breadth x^jV^ 

 inch. 



It is tolerably evident that the symmetrical and very striking 



