ON DEVELOPMENT ETC. OF PHOROXLS. .j4o 



the anterior end of the eolhir cavity {coLrX Below the gaiijjjlioii, 

 the posterior reeess (/>./'.) is .seen to ]n\\v a (■oin])lete wall, that is 

 to say, the posterior septum is tally developed. In the ahove 

 fleure, the two wide s])aees lying on Ixjth sides of the posterior 

 reeess correspond to the two anterior horns of the collar cavity 

 projecting forward (marked b and (/ in the ■wood-cut). And "we 

 can certainly see that on the dorsal side as Avell as laterally there 

 is no distinct partition or continuation of the preoral septum 

 which, according to Mastermax, should entirely divide the preoral 

 and the collar cavities at every point. As the figure shows, the 

 dorsal portion of the mesentery {mes') is decomposed into line 

 protoplasmic processes which join with those of the fihrous mesen- 

 chymes dis^iersed through the preoral cavity. In section, öd c, 

 passing though the middle of the ganglion (the line III-III 

 of the wood-cut), the collar cavities {col.c.) are much wider and 

 have become united below the œsopliagus {œs). The septum (as 

 the wall of the posterior recess, ]).)•.) in this region is a little more 

 definite in form than in the last figure ; the posterior recess (p.r.) 

 is distinct as before. In section 59 d passing through the line 

 IV-IV of the wood-cut, the posterior wall of the recess (79. y.) is 

 obliquely cut and appears in the right-hand lower corner as a 

 membraneous slice, the recess being distinctly boundetl by the 

 septum {mes\). Outside of it are seen, one on each side, the 

 sections of the retractor nuiscles (ret.), of which more will be 

 said later. The collar cavity (eol.c.) is now very spacious, but the 

 septum laterally remains in the same condition as before. 



From the above descriptions, it will be clear that the preoral 

 septum is complete only in the median ])ortion (indicated by the 

 full line e d ef in the wood-cut), while in the more lateral part 

 on each side, it is at the best a loose open reticular membrane, 



