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formation and further successive development of these organs. It is however by no means 

 necessary to depend only on such growing arms for opportunity of studying the develop- 

 ment of the pedicellarise. This investigation may be executed quite as well, and much more 

 easily, on any developed arm-, as, throughout the whole life of the animal, there seems to 

 be a continual new formation of these organs, especially on the cuticular sheaths of the 

 spines of the arms. 



On examining more closely the cuticular sheath of one of the long spines of the arm. it 

 will be found that the pedicellarire in this exterior part are all fully developed and of the struc- 

 ture above described; while those nearer the base become gradually more rudimentary, until at 

 last one can only observe a layer of simple cells surrounding the root of the spine (see fig. 31). 

 This simple stratum of cells is the starting point for the progressive development of the 

 pedicellarise from the base. In the interior of the cells the development of the 3 calcareous 

 particles above described can be very distinctly traced. They appear first (fig. 32) as 3 

 small widely separate granules situated in one row, and all nearly of the same size. Then 

 the 2 outside granules which represent the side-pieces develope themselves more rapidly 

 than the middle-piece, and soon assume a distinct triangular form (fig. 33) while the middle- 

 piece still appears only like a little indistinctly angular granule. 2 of the 3 corners of the 

 side-pieces now increase (see fig. 34) rapidly in length, developing themselves each in its 

 manner; so that it can soon be discerned which of them is to form the proper forceps, and 

 which shall become the lower plate-shaped process; but the 3 rd corner is relatively less 

 developed, and only increases a little in breadth so as to form the vertical dentated edge 

 projecting inwards from the middle of the side-pieces. The middle-piece now begins also 

 to develope itself, by the extrusion in different directions of 4 cylindrical processes, 2 longer 

 and 2 shorter, whereby it acquires, when viewed from above, the form of an irregular cross. 

 In the subsequent development (see fig. 35) the 2 processes issuing from the side-pieces 

 increase more and more in length, bending inwards towards the media! line. They are 

 however quite simple, without teeth or plate-like enlargements; the upper one truncated at 

 the extremity; the lower, conically pointed. The upper process, or the proper forceps, soon 

 begins however (see fig. 36) to assume its characteristic spade-like form: and from each side 

 of the truncated extremity, there protrudes a sharp corner, forming the exterior tooth of 

 those which subsequently appear. The middle-piece now changes its form rapidly: small 

 processes beginning to grow from the lower side, and again connecting themselves by 

 their extremities, forming thereby the commencement of the perforated plates which 

 subsequently appear, and which serve for the insertion of the motor muscles of the side- 

 pieces. In the same manner the hitherto simply conical processes of the 2 side-pieces 

 afterwards begin also little by little (see fig. 37) to assume their definitive plate-like form; 

 as small processes issue from their exterior sides, and finally connect themselves by the 

 extremities, so as to circumclude the characteristic oval apertures, in the periphery of which 



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