Ceo. C. rriec 



123 



tlio niyolomos, and, in tlie one case above nolc^il, ilici'c is ncluiil coii- 

 tiiunty. In segments fifty-onc to sixty-seven on the right, and in forty- 

 tlireo to sixty-five on the left, the nephrotomes and myotomes are sepa- 

 rated by narrow, artificial spaces. In segments sixty-eight to seventy- 

 five on the right, and in sixty-six lo scventy-l'onr on the loft, tlio nephro- 

 tomes are joined to the outer end of the myotome. It seems fair to 

 su2)pose that in earlier stages all the nephrotomes would be found con- 

 nected with myotomes, but this could be proved only by the examination 

 of a younger embryo. 



A brief account of the fornuition of the splanclmocd'! will now be given. 

 This arises in the lateral mesoblast as small rouiuhnl s})aces (Fig. 11) 

 which grow togetlier, and thus form a continuous cavity on either side, 

 and at the same time split the lateral mesoblast into somatic and splanch- 

 nic layers. (No reference is here made to the pericardial cavity.) The 

 entire coclom of the right side, both nephroca^ls and splanchnococl, was 

 reconstructed on millimeter paper, and this shows that tlie region of 

 most active formal ion is in segments nine to 

 fifty-three. In segments (ifty-four to iifiy- 

 seven it is almost absent, while back of this 

 it is entirely absent. Fig. 13 shows the 

 crelom in three segments, the heavy lines indi- 

 cating the boundary of the nephrocoels, and 

 the light tliat of the splanchnocoel. No at- 

 tempt is made to show anything beyond the 

 outline^ of the cavities. It will be observed 

 that the divisions of the splanchnococl com- 

 municating with the nephrocoels have a sort 

 of segmental character, and that the cavity 

 in one segment in no case quite communi- 

 cates with that in the next. Further forwai-d, 

 however, such commu2iications do occur, in 

 one instance the cavities in four consecutive 

 segments being joined together. 



In a few cases a splanchnocoelic cavity was found lying just beyoml the 

 nephrococl, but without any communication between them. In others, 

 as in Figs. 13 to 15, the two are seen to be breaking into eacli otlier. 

 This may not be the only way in which the communication between the 

 nephrococl and s])lanchnocncl is established; in some cases (Fig. 1, right 

 side) a splitting seems to l)cgiii at the nc|)liroc(pl and extend oiitwai'd into 

 the lateral mesoblast. 



The next embrvo to which attention will be called is between tlie one 



l''l(). 12. I{('c()ii>l-niil ion of 

 (In- ('(rloiii ill llircc si'jfmciils ol' 

 an (^iiil)c.\() ill which ( li(^ spill iicli 

 nocMi'i is ill Mil (iiirly stiitro of 

 loriiiiitioii, iiiiido (111 iiiilliiiuitor 

 piilicr. 'I'lic iK'iiiiroiMi'l, /((', Is 

 boiiiiilcMi by t lie hon\y line, and 

 th(^ sphiiK.'hnocii'i hy (he liK'lit. 

 NotliiiiK' is shown lioyoiKl tlio 

 outline ol' tiie cavities. 



