30 SUMMARY OF CURRENT RESEARCHES RELATING TO 



mesoderm or primary mesoderm, from which arise the mesodermic head- 

 organs in front of the hyomandibular cleft, is entirely due to cephalo- 

 genesis. A detailed account is given of what haj)pens on each day. 



J. A. T. 



Development of Vertebral Column of Megalobatrachus. — J. P. 

 De Gaay Fortman {Tijdschr. NederJand. Dierk. Ver., i;»18, 16, 

 121-62, 2 pis., 10 figs.). In this giant salamander there is a hint of 

 an intervertebral cleft. In the place of the spinous processes there are 

 closing pieces of connective tissue, which are continued into the 

 arcualia of two vertebra and form by their union the pre- and post- 

 zygapophyses. Between the centra there is no cartilaginous joint, but 

 a broad ring of connective-tissue cartilage. This is continued far into 

 the centrum and forms eventually a very delicate cartilaginous zone. 

 The intervertebral cartilage arises in the notochord itself, wliich is 

 constricted intra-vertebrally and continued inter-vertebrally. The 

 vertebra of Amphibia are referable to fish vertebrge in which there has 

 been fusion of two arcualia. Half of the first segment forms cartilage, 

 which takes part in forming the condyles and the bases of the arcualia 

 of the first vertebra. The boundary between occipital and atlas is in 

 this first half-segment. The first vertebra is, as regards arcualia, more 

 than one vertebra, for three sclerotome halves share in its making. Parts 

 of the atlas and of the condyles are the equivalents of Albrecht's pro- 

 atlas. ■ J. A. T. 



Eel with Left Eye in Lower Jaw.— C. E. Droogleevbr Fortuyx- 

 VAN Leyden {Tijdschr. Nederland. Dierl. Ver., 1918, 16, 271-9, (5 figs.). 

 A curious abnormality in a common eel about 30 cm. in length. The 

 left eye was situated on the under surface of the lower jaw, a little 

 to the left of the middle line, and had a normal structure. At the 

 spot where the left eye should have been there was a small dimple. 

 It is probable that the optic vesicle grew out anteriorly and towards 

 the ventral surface, instead of laterally ; that it reached and traversed 

 the anterior mesodermic mass ; and that it continued growing until it 

 reached what afterwards became the epidermis of the lower jaw. It is 

 probable that the epidermis reacted to form a lens and cornea. It 

 is probable that the primordia of the eye-muscles, applying themselves 

 at a very early stage to the capsule of the eye, were gradually led as they 

 developed to their extraordinary final position. J. A. T. 



Eye-displacement in Pleuronectids.— Otto T'au.o{Zool. Anzeir/er, 

 1920, 51, 119-42, 12 figs.). In young flounders, plaice, and the like, 

 the two eyes are for a considerable time symmetrically disposed, one on 

 each side of the head. The young fishes swim vertically till they are 

 10-15 mm. long, when they lie on one side on the sand. At this stage 

 the lower eye may be lost by friction. It may be noted that there are 

 blind, genera {Soleotalpa, Apionichthys and others). The friction of the 

 sand causes cramp-like contractions of the eye-muscles, which lift the 

 eye to the other side of the head. The change takes place in three 

 days or so. Its mechanism is analysed. The gap is filled with support- 

 ing tissue, partly ossified. The musculus rectus externus degenerates 



