334 JOHN BEARD, 



number of trunk somites was kept, and this happens to be the only 

 specimen of exactly this size in the collection. There are probably 

 from 75—80 trunk somites present. This may be concluded from the 

 number of gill-pouches: of these four are present and the first bran- 

 chial is open to the exterior. There is a slight olfactory depression. 

 The optic vesicles are constricted but not yet invaginated. The 

 mouth communicates with the gut, and one gill-pouch is open to the 

 exterior. The auditory organ is an open cup with narrow aperture. 

 The pronephros is fully formed, but the segmental duct ends in the 

 epiblast some distance in front of the anus. 



In the spinal cord the transient ganglion-cells have not all as 

 yet become ganglionic, and, in comparison with embryos but sligthly 

 older, the nerve-fibres of the transient system are somewhat feebly 

 represented. None the less notable appearances are to be met with. 

 The figure (Fig. 18) of a transverse section taken just in front of the 

 pronephric region (the section cuts the first nephrostome on one side 

 near its anterior border) establishes the following. Several large 

 ganglion-cells (gl c.c), roofing in the cord, pass or flow into a number of 

 similar ganglion-cells (w.gl.c) forming a bridge from the cord to the 

 tip of the myotome. Whether from these latter a nerve proceeded 

 outwards and onwards could not be determined in the present case. 



In the following sections the roof of the cord is seen to be 

 largely made up of cells, which, like those figured in Figs. 2 and 5, 

 are developing ganglionic characters. 



Here and there a transient nerve (n.p), reaching to the myotome 

 and even extending beyond it between myotome and epiblast, can be 

 detected (Fig. 19). 



There are several other sections in the series like that figured. 

 A slightly different picture is furnished by a section further caudnl- 

 wards. In Fig. 20 three large ganglion-cells {gl. c.c) bulge out in the 

 roof of the cord, while a fourth and fifth {sp. c) to the left of the 

 figure, are being largely used up in the formation of a nerve. 



This series is further remarkable for the number of karyokinetic 

 figures it contains. 



In embryo No. 129 there are 76 somites behind the last gill- 

 pouch. There are 4 gill-pouches and of these the first branchial is 

 open. The embryo is about 8 mm in length. The optic vesicles 

 reach the epiblast and are slightly constricted. There is no sign of 

 a developing lens. The auditory involution is widely open, and its 

 epithelium is rapidly proliferating. The segmental duct ends in the 



