PROTOSTIG-MATA OF MOLGULA IFANHATTENSIS. 159 



f]XPLANATIOX OF PLATE 9, 



Illustrating- Mi-. Artliur Willey's paper '' On the Protostig- 

 niata of Molg-n 1 a inanhattensis (De Kay). 



Letters of Reference. 



at. Atrial or cloaca! orifice. Boj. Ori;au of Bojanus (renal organ), c. Cardio- 

 pericardiac vesicle, cc. Central canal of medullary tube. cv. Cerebral vesicle 

 with pii^nient-globule. d.t. Dorsal tubercle, end. Endostyle. ep. Ecto- 

 dermal processes, e.v. Eiidoderniic vesicle. /. Follicle, rj. Ganglion, m. 

 Mouth, n. Notochord. o.e. (Esophagus and its orifice, jh b. Peri|)haryngeal 

 band. j).L Prstoral lobe (organ of fixation), sn.y. Subneural gland, st. 

 Stomacii. t. Tail. l.b. Tongue dividing cleft, t.c. Testa cells, v.t. Vascular 

 trabecula. 



All the figures refer to Molgula manhatt ensis. 



Fig. 1. — Anterior portion of urodele larva (tadpole) after hatching. 

 Zeiss 3 D. 



Fig. 2. — Urodele larva undergoing precocious metamor|)hosis witiiin the 

 follicle. Tiie tail is seen in regression at its insertion into the body, where 

 there is a mass of hislolytic residua. 3 D. 



Fig. 3. — Distigniatic stage, after fixation. A and B are the two ])rimordial 

 stigmata. The pigmented globule (eye-spot) marks the position of the cerebral 

 vesicle now in regression. 3 1). 



Figs. 4 — G. — Successive stages in the growth of the jirimordial stigmata of 

 the right side. 



Fig. 7. — Condition of protostiginata rather later than that shown in Fig. G, 

 from the left side. 



Fig. 8. — Commencement of the tetrastigmatic stage from the left side. 

 Between the mouth and the peripharyngeal band are seen four pericoronal 

 tentacles. 3 A. 



Fig. y. — Protostigmata of preceding. 



Fig. 10. — Composite diagram illustrating the mode of origin of the six 

 protostigmata. [From Willey, ' Amphioxus and the Ancestry of the Verte- 

 brates,' 1894, p. 233.] 



Fig. 11. — Protostigmata of the right side at the hexastigmatic stage. 



Fig. 12. — Entire individual viewed as a transparent object at the hexastig- 

 nuiiic stage. The first protostigma has become subdivided into four secondary 



