240 SIDNEY F. HAEMER. 



mal or distal rosette-plates may be of the typical number 

 (two), situated on the basal side of the insertion of the cal- 

 careous lamina, or each of these may fragment into as many as 

 three pieces placed close together (fig. 33). In S. truncata, 

 although the typical number of lateral rosette-plates may occur, 

 one zooecium was noticed to have three vertically arranged 

 rosette-plates instead of the usual horizontal series of four. 



It is obvious from what has been said that the relation of 

 the distal rosette-plates to the line of insertion of the crypto- 

 cyst is not the same in all species. In those in which the 

 cryptocyst joins the distal wall at some distance from the 

 base the distal rosette-plates are typically found, one beneath 

 the floor of each lateral recess (fig. 33). In species in which 

 the cryptocyst joins the basal wall the rosette-plates of the 

 distal wall are of course entirely distal to its insertion. The 

 subopercular cavity is in fact part of the body-cavity, what- 

 ever the relation of the cryptocyst, and the distal rosette- 

 plates maintain their position irrespective of the behaviour of 

 the cryptocyst. 



Methods employed. — For the examination of the muscular 

 system I have found it convenient to remove the basal wall 

 of the zooecia. This may easily be done by embedding a 

 piece of spirit material (not decalcified) in paraffin, and 

 cutting away the basal wall with a scalpel after the paraffin 

 has cooled. On dissolving out the paraffin the zooecia can be 

 stained and mounted in Canada balsam. The removal of the 

 basal wall greatly facilitates the examination of the internal 

 anatomy of the zooecia. 



The preparation of the opercula has been made by the 

 following method, which has enabled me to obtain satisfac- 

 tory evidence of the structure of small unique specimens 

 without in any way destroying their value. The fragment 

 of the colony is boiled for two or three minutes in a 4 per 

 cent, solution of caustic potash (although a stronger solution 

 might be used with impunity). The opercula are then brushed 

 off, or if necessary, removed, with the epitheca, by the aid 

 of a needle. The calcareous parts are washed and reserved 



