Fig. 7. A series of diagrams of transverse sections through Peripatus 

 embryos to show the relations of the coelom at successive stages. 

 (After Sedgwick.) A. Early stage. 1, gut; 2, mesoblastic 

 segment ; no trace of the vascular space ; endoderm and ectoderm 

 in contact. B. Endoderm has separated from the dorsal and 

 ventral ectoderm. The segment is represented as having divided 

 on the left side into a dorsal and ventral portion. 1, gut; 

 2, somite ; 3, haemocoele. C. The haemocoele (3) has become 

 divided up into a number of spaces, the arrangement of which is 

 unimportant. The dorsal part of each somite has travelled 

 dorsalwards, and now constitutes a small space (triangular in 

 section) just dorsal to the gut. The ventral portion (2') has 

 assumed a tubular character, and has acquired an external open- 

 ing. The internal vesicle is already indicated, and is shown in 

 the diagram by the thinner black line. 1, gut; 2', nephridial 

 part of coelom ; 3, haemocoele ; 3', part of haemocoele, which 

 will form the heart the part of the haemocoele on each side of 

 this will form the pericardium ; 4, nerve-cord. D represents the 

 conditions at the time of birth; numbers as in C, except 5, slims 

 glands. The coelom is represented as surrounded by a thick 

 black line, except in the part which forms the internal vesicle of 

 the nephridium. 



