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ADAM SEDGWICK. 

 IT 



Fig. 2. — Various stages in tlie development of Phallusia mammillata 

 (from Huxley ; after Kowalewsky). I. Commencing gastrula. fh. Seg- 

 mentation cavity. II. Late gastrula stage, eo. Blastopore, ch. Note- 

 chord, dd. Hypoblast. III. More advanced embryo, n. Neural tube- 

 e. Epiblast. IV. Formation of neural tube completed, dd' . Hypoblast 

 in tail. m. Muscles. V. Larva just hatched, the end of the tail is not 

 represented, a. Eye. gb. Dilated extremity of neural tube, with otolith 

 projecting into it. Ug. Anterior swelling of spinal division of neural 

 tube. /. Anterior pore of neural tube. Bm. Posterior part of neural 

 tube. 0. Mouth, chs. Notochord. kl. Atrial invagination, dd. 

 Branchial region of alimentary tract, d. Commencement of oesophagus 

 and stomach. dd\ Hypoblast in tail. m. Muscles, h'p. Papilla for 

 attachment. VI. Body and anterior part of a two days' larva. 



