484 W. WOODLAND. 



of the plate I sliall term the base, and the opposite, more 

 obtuse region the apex. In side aspect it can be seen that 

 the handle of the anchor and the base of the plate form a dis- 

 tinct joint, the one with the other (fig-, 25), and the anchor 

 and the plate rotate upon each other at this joint, the angle 

 included between the two in consequence vai'ying in magni- 

 tude (Ostergren, 4), It can also be observed in side view 

 that the arms of the anchor bow do not lie in the same plane 

 as the shaft, but in a plane slightly more inclined towards the 

 dermal layer, i.e. more nearly parallel with the plane of the 

 plate (text-fig 1). 



Respecting the general arrangement of the spicules, it is 

 an obvious and noteworthy fact that the major axes of these 

 plate-and-anchor spicules, as they lie in the body-wall, are 

 disposed transversely to the long axis of the animal, so that 

 in a transverse section of Synapta the spicules are seen in 

 side aspect (text-fig. 1). Further, although the spicules never 

 assume, as regards their major axis, other than a transverse, 

 or approximately transverse, disposition in the body-wall, it 

 is quite a matter of chance as to whether the bow of the 

 anchor and apex of the plate of each spicule lie to the right 

 or to the left of the observer; in other words, they are disposed 

 pretty equally in both positions. 



A few words concerning the preparation of Synapta material 

 for the study of the spicule development are necessary. My 

 material was obtained from Naples, and consisted of specimens 

 of the two species — Synapta inhterens and S. digitata. 

 My specimens of S. inhajrens averaged 1 cm. to 1'5 cm. in 

 length, and they were specially prepared for me by the osmic 

 acid and picro-carmine method described in Study IV, e. g.^ 



* lam indebted to Dr. P. Mayer for recoiiimendiug me liis picro-magnesia 

 carmine stain as a substitute for tiie Ranvier and Weigart preparations. The 

 objection to these latter is their inconstancy of composition — the free ammonia 

 evaporating and the carmine being preripitatcd ; an excess of free ammonia of 

 course tends to macerate the tissues. I must say, liowever, that with one 

 exception I have always used Ranvier and Weigart with perfect success, and 

 so long as free ammonia is absent there is little objection to them, at least in 

 practice. 



