THE MALAYAN SPECIES OF ONYCHOPHORA. 85 



riidimciitarj myotome, and consequently a developing outgrowtli, wliicli later 

 on becomes separated off as the appendicular portion of the somite. 



Figs. 15 a and 15/5 (x 170). — These figures represent transverse sections 

 of an embryo about the same age as that shown in Fig. 5. The generative 

 portions of the somites situated on either side have almost come together on 

 the dorsal aspect of the mid-gut. The splanchnic walls, which, owing to a 

 slight change of position, have become ventral, have considerably thickened, 

 and the germinal nuclei are gradually becoming excluded from the coelomic 

 cavity, that is the ovarian cavity. 



Fig. 15 a. — This figure shows a section passing through the fourth somite 



from the posterior end {sopk'^-^). 

 Fig. 15 6. — This figure shows a section passing through the fifth somite 

 from the posterior end (som.^-*). 

 Figs. IQa, 16 6, and 16c (X 170). — These figures represent transverse 

 sections of an embryo slightly older than that shown in Fig. 5. 



Fig. IGtf. — This figure shows a section passing through the third pair of 

 somites from the posterior end (aow."'), that is the somite of the 

 genital ducts, 'i'lie somites in question, which are devoid of germinal 

 nuclei, have not yet entered into communication on the dorsal aspect, 

 nor have they at their outer ends fused with the ectoderm of the 

 ventral surface. Note the large blood-spaces situated on either side 

 and ventral to the proctodsEum. 

 i'ig. 16 li. — This figure shows a section passing through the fourth pair of 

 somites from the posterior end {som. »■'), Note the germinal ridges 

 {//fi. r.) placed in the ventral wall of the ovary, and the double ovarian 

 cavity situated above the ridges. The whole structure is fused to — if 

 it does not form a part of — tiie ventral wall of the pericardium {p.c). 

 Fig. 16 c. — This figure shows a section passing through the fifth pair of 

 somites from the posterior end {som.*'*). It presents the same 

 characters as the somite shown in the previous figure, except that the 

 germinal ridges are mucii more strongly developed. 

 Figs. 17 a, 17 fj, and 17 c (X 170).— These figures represent sections of an 

 embryo which is considerably older than the one sections of which are illus- 

 trated in Figs. 16 a, b, and c. 



F'ig. 17 «. — This figure shows a section passing through the third pair of 

 somites from the posterior end (^oct."--). The somites have fused on 

 the dorsal aspect to form a kind of median chamber, the walls of which 

 are devoid of germinal nuclei. 

 Fig. 17 h. — This figure sliows a section passing through the fourth pair of 

 somites from the posterior end (w///. »•''). It illustrates (he germinal 

 ridges {ge.r.) situated on the ventral wall of the ovary, and separated 

 from tiie dorsal wall by the slit-like ovarian cavity {pv. c), and the 



