PERIVISCERAL FLUID OF ECHIXODERMS. 241 



lacunae and continuous with the peripheral prestereomal areas 

 which enclose the stereom of the adjacent region of the body wall. 

 The "amoebocytcs with spherules" are very few in this region. 

 Thirdly, the definitive regenerated stereom which is crystalline 

 in character, devoid of nuclei and in the lacuna- of which there 

 are no "amcebocytes with spherules." 



It i- obvimis that the cellular elements which form the mem- 

 brane have either been derived directly from cells in the region 

 of the pre-tereomal area- or from cell- of the peri\ i-ceral fluid 

 which ha\e migrated to tin- ...iva and formed -yncytia. Since 

 the leu 'lit- only cells of the peri\ i-<vral thiid which 



have l.ft-ii ob-rrved to form -yncytia and since they are the 

 COenCXT initial wandering mt-eiichym.il cell>, then is 



on t" suppose thai they h.i\ t- -on ie part in this process. That 

 com formation doc- not nece ai ilv -tart from the cut >ur- 



idenccd by t hi- appear. ince of indc- 



pemlt-i illation in the membrane I 



A more detailed -ludy of ilu- n l.iiioii^hi| >- of the K-u- -to the 



Deration of tin- te-t i- to b- more closely followed in a more 

 eMi-ntlt'l ' riim-i 



These observation neral \\ith Tin > :iciu>ion^ 



that tl. obl.i-tic cell- "oii^ht to \ 'K'd .inion^ the true 



pla^ma-amo i 3, though t!n-\ are di-Minilar ,i- to their 



functional manife>tation-. an<l t oii-e<|iient Iv, too, as to their 

 i hentic. il ( on-titution. ! i unlikely that their (]iialit\ ot 



taking ii]> a >ii])ertluit\ of inor^.iiii. -.ilt- from the Mirroimdini; 

 medium ha- inlhu-nced the cell-, their power of anneboid move- 

 ment haxill- been Ml|)|ire--ed or limited." Me conclude- that 

 the direction- of the p-eiidopodi.t predetermine the characteri-tic 

 piotru-ioii- of the cr\-tal- in I'^olns p>h<i utapiis. The cr\-ial 

 wlu-n formed Occupies the whole of the cell except for a -mall -pace 

 occupied by the nucleii-. In the formation of the >tereom in 

 6'. ilrobachicnti* a -imilar predetermination of the or^ani/ation 

 of the skeletal element- is apparent in the pre-tereonial area-. 



I'rom the above observation^ it may be concluded that the 

 leucocNte- in both the active and passive phases are those celU 

 which are of conMaiit occurrence in the Echinoderm-. The\' are 

 phagocytic, thrombocytic and possibly scleroblastic. These 

 cells are omnipre-ent in all regions of the perivisceral cavity. 



