48 Mr. E. A. Minchin. Note on the Larva and the 



The two component layers very soon begin to undergo changes of 

 form and structure, which are best described separately, since the two 

 layers develop more or less independently of one another, and a given 

 stage in the development of one layer is not always found combined 

 with one and the same stage in the development of the other. 



The dermal layer becomes divided (fig. 5) into two kinds of cells r 

 (a) cells which retain the original form and characters and remain on 

 the surface, and (b) cells with smaller nuclei, which sink below the 

 outer epithelium and form a scattered layer between it and the 



FlG. 5. Section of stage about twenty-four hours after fixation. The left side is 

 represented as slightly in advance of the right side. 



gastral cells. The former (a) secrete each a single monaxon spicule, 

 which appears first on the inner side of the nucleus, but soon grows out 

 and projects free from the surface. The latter (6) unite into groups 

 and secrete the triradiate spicules. The monaxons appear first, as in 

 Sycandra raplianus* and begin to appear about twenty-four hours 

 after fixation, the triradiates about twelve hours later. The dermal 

 layer has thus become divided into two parts, which gradually assume 

 the adult characters. I have not observed the origin of the pores. 



The gastral layer, at first a compact mass with no definite arrange- 

 ment, soon begins to form a cavity (fig. 5). The cells assume a 

 radiate arrangement, and a split-like lumen appears in the centre. 

 Sometimes two or more such lacunar spaces arise, at first quite 

 independent of one another, but later fusing to form a single gastral 

 cavity, which soon becomes very large, causing the larva to increase 

 considerably in size as a whole. At first the cavity is surrounded on 

 all sides by gastral cells, but as it increases in size a spot appears 

 where gastral cells are wanting, and the cavity is limited only by 

 dermal cells (fig. 6). This is the region of the future osculum, and 

 the dermal cells at this spot form the future oscular rim, where collar 



* Metschnikoff, loc. cit. 



