DEVELOPMENT OF BALANOGLOSSUS KOWALEVSKII. 533 
Fie, 110.—Transverse section of young ovary of B. Kowalevskii (young 
adult). Obj. D, oe. 2. 
Fig. 111.—Group of ovarian follicles of B. Kowalevskii, older than the 
above. Obj. D, oc. 2. 
Fie. 112.—Ripe ovarian follicle of B. Kowalevskii. Obj. A, oc. 2. 
PLATE XXXIII. 
Diagrams.—Skin coloured light blue; nervous system, dark blue; 
hypoblast, light red; blood-vessels, dark red; mesoblast, green. 
Fic. 1.—Blastosphere. 
Fie. 2.—Gastrula. 
Fic. 3.—Longitudinal vertical section through gastrula; blastopore being 
nearly closed. 
Fic. 4.—Ditto ; blastopore closed. 
Fig. 5.—Ditto, later stage; mesoblast forming. 
Fie. 6.—Longitudinal horizontal section through a somewhat later stage. 
Fie. 7.—Longitudinal horizontal section through larva in Stage G. 
Fic. 8.—Transverse section of collar of foregoing in plane of line d d. 
Fic. 9.—Longitudinal vertical section of Stage H. 
Fie. 10.—Transverse section of collar of foregoing in plane of line d d. 
Fre. 11.—Longitudinal horizontal section of adult in plane of heart. (This 
plane would not really take in the periheemal cavities, but their relations are 
thus made clear.) 
Fig. 12.—Transverse section of foregoing in plane of line d d. 
Fre. 13.—Longitudinal horizontal section of junction of collar and trunk in 
a larva of about 4 gill-slits, 
Fic, 14.—Similar section to foregoing of adult, showing formation of oper- 
culum, atrial cavity, and collar funnels. 
