544 
EDWIN S. GOODRICH. 
opening to the exterior on the left side, in front of the mouth. 
The ectoderm round the opening sinks in to form a deep 
groove and depression — the preoral pit. The cells lining the 
original left ccelomic sac, now known as Hatschek's pit, are 
broad, with a rounded nucleus and a bunch of cilia. The 
Text-fig. 2. 
Reconstruction from transverse sections of a thick slice of the 
head of an embryo of Torpedo, 10’5 mm. long. Anterior view. 
f.b. Forebrain, h.b. Hindbrain, h.y. Hypophysis, n.t. Noto- 
chord. o.l. Olfactory sac. o.p. Optic cup. p.c. Premandibular 
somite, p.t. Premandibular tube, or canal opening into the 
hypophysis. 
cells lining the preoral pit are probably of entirely ectodermal 
origin, and acquire a slender, elongated shape with an oval, 
deeply staining nucleus and a single flagellum. In later 
stages they appear to invade the pit of Hatschek, becoming 
specialised into the rod-bearing cells. As the larval mouth 
