34 ANATOMY AND PHYSIOLOGY 



its development it has the appearance of a slender inequi- 

 biclavate cylindrical spiculura (as represented in Plate III, 

 Fig. 73) ; in the next stage there is a slight indication 

 of the spinulate base, and a corresponding amount of 

 expansion of the apex, but no indication of the radii 

 (Fig. 74). From this state to the next well-marked stage 

 of growth (represented in Fig. 75) the progressive develop- 

 ment of the radii may be readily traced, and thence to the 

 adult condition represented in Fig. 76. 



In its fully-developed state we find a great increase in 

 its size in every respect ; the base becomes fully developed 

 and globular, and the radii elongated to a very considerable 

 extent. 



In other instances, where defence alone appears to be 

 contemplated, we do not find these beautiful adaptations 

 for motion in every direction prevail. The bases of the 

 spicula in those cases are abundantly spinous, and are 

 evidently intended to maintain a firm hold by their 

 attachments, and are destined rather to rigidly maintain 

 their position than to yield to any struggling body with 

 which they may be in contact. The numerous spines with 

 which these shafts are frequently covered are calculated to 

 wound and lacerate, rather than to retain the enemies with 

 which they are engaged. 



I have received from my friend, Mr. J. Yate Johnson, of 

 Madeira, a new and very illustrative instance of the combi- 

 nation of defence and aggression in the structure and 

 offices of the internal defensive spicula ; and in this case it 

 is not a new organ, but an adaptation of a well-known 

 form to a new purpose, in the shape of a contort trenchant 

 bihamate spiculum of unusual size and structure. In the 

 course of my examination of the results of the deep-sea 

 soundings in the Atlantic, I found several of these spicula, 

 and was much interested by the singularity of their struc- 

 ture, which at that time I could not comprehend. 



The general outline is much like that of the type-form 

 so commonly found imbedded in the sarcode, but it is 

 somewhat less flexuous in its curves, and the shaft and 

 hami are very much larger and stouter than those of the 



