129 



dorsal hollow outgrowth from the brain. In the young animal 

 the olfactory pit opens by the neuropore into the central canal 

 (Fig. 80, A), but that passage is closed in the adult. Possibly 

 the olfactory pit is homologous with the hypophysis or pituitary 

 body of Vertebrates, the homologue of which in Tunicata has a 

 ciliated funnel. Finally, the median cere- 

 bral eye (Figs. 80 and 81) is a mere pigment 

 spot in the anterior wall of the cerebral 

 vesicle, and a series of somewhat similar 

 pigment spots occurs along the floor of the 

 central canal in the spinal cord. 1 There is 

 no known auditory organ. On the under 

 surface of the oral hood patches of ciliated 

 epithelium drawn out into rounded lobes 

 were called by Johannes Mliller the " Ea'der- 

 organ." This is probably of use in drawing 

 water inwards to the pharynx, but it may 

 also be a sense-organ. 



The Gonads are segmentally arranged 

 along the sides of the body, projecting into 

 the atrial cavity at the sides of the pharynx 

 and intestine. In some species the gonads 

 are paired, but in others belonging to the 

 genus Asymmetron (p. 137) only a single 

 series, that of the right side, is present. In 

 the common Amphioxus (Branchiostoma 

 1 anceolatum) there are about 26 pairs (Fig. 70, 

 B), lying in somites 25 to 51; and ovaries FIG. 

 and testes are found in separate individuals 

 in all other respects. Each gonad is sur- 

 rounded by a layer of coelomic epithelium. 

 The gonad must therefore be regarded as hav- 

 ing grown down from a myotome of the body- 

 wall into a coelomic pouch, carrying before it the coelomic and 

 then the atrial epithelium (Figs. 7 2, and 74, A, #). Eventually the 

 gonads, when ripe, burst through the layers of epithelium, and 

 the ova and sperms are shed into the atrium and escape to the 

 exterior by the atriopore, or it may be in some cases by the mouth. 



1 The cerebral eye and the pigment spots of the spinal cord are especially 

 prominent in the oceanic species Branchiostoma pelayicum, Giinther. 



VOL. VII K 



81. Branchiostom a 

 lanceolatum. Anterior 

 portion of central nerv- 

 ous system from above, 

 showing dorsal and 

 ventral spinal nerves. 

 (From Willey, after 

 Schneider.) 



