DEVELOPMENT OF AMPHIUKA SQUAMATA. 133 



be used with the shellac method of mounting, and the danger 

 of staining the mounting agent, as in the case of glycerine and 

 albumen, is avoided. On the other hand, hsematein gives more 

 differentiation. For embryos preserved in glacial acetic acid I 

 used Dr. Mayer^s hsemalaun, which gives a blue nuclear stain, 

 and at the same time colours much of the plasma a faint yellow. 



III. Cutting and Mounting. — Embryos fixed and stained 

 according to my standard method were embedded in paraffin, 

 and cut into series of sections in a plane parallel to the line 

 joining the madreporite with the mouth, and at the same, per- 

 pendicular to the plane of the disc. 



A word or two on their orientation may not be out of place 

 here. The young were in all cases extracted from the mother, 

 and the madreporite found by examination with the dissecting 

 microscope. Then, if the arms were long, all were broken off 

 except that which was opposite to the madreporite; but if they 

 were short and comparatively stiff only this arm was broken 

 off. In the case of my earliest stages, where the arms were 

 undeveloped, it was necessary to break off one point of a pen- 

 tagon, and often it occurred that the animal (if only about 

 •32 mm. in diameter) was destroyed or the breakage went 

 obliquely, so as to mislead one afterwards. In general, out of 

 three series of sections of this stage only one was satisfactorily 

 orientated. This orientation had in all cases (except in the 

 latest stages) to be performed on the living animal. When 

 the animals had been embedded the paraffin was cut away, so 

 as almost to lay them bare on one side, and the position of the 

 madreporite was thus recognised, and the orientation of the 

 block effected. Fresh paraffin was then melted on to the 

 exposed place. 



I must here raise an emphatic protest against the method 

 employed by Cueuot (6), who professes to give an account of 

 the origin of the ovoid gland and its surrounding sinus in 

 Amphiura squaraata, and is naturally quite wrong. He 

 cuts a number of adults containing embryos, and then founds 

 conclusions on casual sections of the contained young. The 

 preserving fluid in this case penetrates neither rapidly nor 



VOL. XXXIV, PART II. NEW SEE. K 



