THE MALAYAN SPECIE8 OF ONYCHOPHORA. 59 



embryo (p. 49). A mesodermal somite which has reached 

 the point of maximum development, but which is still un- 

 modified, is crescent-shaped (PI. 1, figs. 11 a and 12 A;), the 

 splanchnic wall always being less curved than the somatic. 

 Though the somites situated on either side never meet 

 either below or above the gut — except in the formation of 

 the ovary, — at one period in the development they approach 

 very near to one another, especially on the ventral surface, 

 a condition which reminds us of that occurring in an adult 

 Annelid, and at one time must have existed in the ancestral 

 Arthropod. 



By the time the somites liave reached this stage, the rudi- 

 ment of the nerve-cord has attained considerable develop- 

 ment. The rudiment in question, together with the myotome 

 which develops on the latero-ventral aspect of the somatic 

 wall, exerts such a pressure on the somite that the two walls 

 of its ventral portion are pressed together, resulting in the 

 obliteration of the ccelom in that part of the somite. Only 

 the dorsal portion of the coelom, together with the small 

 rudiment of the appendicular outgrowth, remains (PI. 7, 

 fig. 11 h). The growth of the appendicular portion for a 

 time keeps pace with that of the leg, to the distal end of 

 which the coelomic outgrowth reaches. The ultimate separa- 

 tion of the appendicular from the median coelom is 

 brought about by the continued increase in size of the myo- 

 tome, which extends both in front of and below the canal 

 which places the two poi-tions of the cojlom in communi- 

 cation with each other. I have been unable to observe the 

 septum which Mr. Sedgwick describes as growing from the 

 ventral wall, and finally dividing the coelomic cavity into 

 median and appendicular portions, and I am firmly con- 

 vinced that the obliteration of the communication is brought 

 about in Eoperipatus by pressure from without, the result 

 of the continued growth of the myotome and nervous system. 



The median portion of the coelom persists for a short 

 time after the appendicular part has been constricted from 

 it, but it soon disappears, leaving absolutely no trace of its 



