THE MALAYAN SPECIES OF ONYCHOPHORA. 81 



layer is quite distinct from the central mass of yolk, though it contains food 

 material in the form of lar^e round yolk-bodies, as well as numerous small 

 refringent bodies, which stain like the yolk. 



Fig. 10 a. — This figure represents the twelfth transverse section in the 

 series, counting from the anterior end. It passes through the first 

 pair of somites {som}). On the left, above the somite, there is a small 

 cavity which does not exist on the other side, where there are only a 

 few nuclei, which may possibly represent a rudiment in which a cavity 

 similar to the one already existing on the left; side will appear later in 

 the development. The centre of the section is occupied by the endo- 

 derm (e«.) of the anterior end of the embryo. The thickened portion 

 of the ectoderm, situated on the latero-ventral aspect, is the rudiment 

 of the brain. 

 Fig. 10 h. — This figure represents the third transverse section behind the 

 one shown in Fig. 10 a. It passes through the anterior limit of the 

 central yolk [c.y) and the posterior limit of the endodermal wall of the 

 anterior end of the embryo. The small cavity found in Fig. 6 a has 

 disappeared, a fact which proves that the cavity in question does not 

 represent the anterior portion of the second somite. 

 Fig. 10 c. — This tlgure represents the tenth section behind the one shown 

 in Fig. 10 i. It passes through the posterior end of the first somite 

 {som}), the middle of the second somite {som'?), and, on one side, the 

 anterior edge of the third somite {som?), which passes forward above 

 the second somite. The central yolk {cy.) is quite distinct from the 

 endodermal layer, and contains no nuclei. At the bottom of the 

 section, at a point which is situated quite close to the anterior edge of 

 the blastopore, the endodeim is being recruited from the undifferen- 

 tiated cells {en. in.). 

 Fig. 10 d. — This figure represents the eighth section behind the one 

 shown in Fig. 10 c. It passes through the anterior end of the blastopore 

 {ant.b.p.) and the second and third pairs of somites {som?, som?). It 

 shows the yolk {ex.y) protruding from the blastopore and spreading 

 over the lower aspect of the section. The central yolk (c. _y.) and 

 endoderm (c?/.) have the same appearance as in Fig. 6 c, the former 

 being absolutely devoid of nuclei. This section shows the ingrowtii 

 at the edge of the blastopore to form the endoderm {en. in.). The 

 mesoblastic somites are quite distinct and separate from this ingrowth. 

 Fig. 10 e. — This figure represents the eighth section behind the one 

 shown in Fig. 10 d. It passes through the region where the lips of the 

 blastopore have fused {^mid. b.p.), the third somite {som?) on one side 

 and the fourth {som.^) on the other having been cut. 

 Fig. lOy. — This figure represents the ninth section behind the one shown 

 in Fig, 10 e. It passes through the posterior moiety of the blastopore 

 VOL. 45, PAUT 1. — NEW SERIES. F 



