of the Fishery Board for Scotland. 



surface of the head, while the second branch opens by a pore on the 

 ventral surface of the same (fifj. 24) ; this anterior prolongation of the gut 

 is not present in all species. Thus, in the embryo of the hake (Merluccius 

 vulgaris), when it is ready to hatch, the gut does not extend further forward 

 than the level of the pre-opercular apertures. In no case was a connection 

 between the gut and Kuppfer's vesicle distinctly made out. 



In later embryonic stages it is very often difficult to see the ciliated 

 portion of the gut (viz., in the pectoral region). This fact is dne to the 

 great development of tissue which goes on ventral to the gut in that part. 

 Thus, in an egg '9 mm. in diameter (probably belonging to the Mugil 

 species), the gut shows a very distinct, though very delicate, limiting wall. 

 At first sight the gut seems to end at the level of the junction of the 

 two lateral arteries (branchial veins) ; but that fact is due to the thick 

 plate of tissue lying ventral to and obscuring the sesophageal portion of 

 the gut. The £esophageal ciliated portion could be made out with diffi- 

 culty. In the embryo of the dab (Pleuronedes limanda) similarly the 

 gut appeared to end short of the pectoral region. 



In other embryos — e.g., that of anchovy — the ciliated portion of the gut 

 is not easily seen owing to the great translucency of the tissues; and so 

 the ciliated portion of the gut is seen earlier in one species than in another.. 

 This is probably not due to the cilia actually appearing at a later stage in 

 the latter. In the case of a very translucent embryo it is only in later 

 development that the tissues attain a density sufficient to cause the cilia to 

 become visible by contrast. 



In the embryo of the plaice, when two-thirds developed, the pectoral 

 filaments have the appearance of a collection of large cells loosely packed 

 together, with channels running from them (p./., fig. 20) ; it is not 

 improbable that these are cells of the epiblast of the yolk sac. In an 

 embryo ready to hatch the pectoral filaments have a resemblance to 

 fine reticulations somewhat similar to minute canals. Posterior to the 

 pectoral regiou there are fine reticulations on the yolk alongside the 

 embryo ; they are probably the rudiments of the pectoral and pelvic fins. 

 At this stage the walls of the dilatation of the gut (stomach) are thickened 

 very much, taking on the structure of the larval gut. The gut is con- 

 tinued posteriorly along the base of the marginal fin, apparently breaking 

 up into a number of thread-like tubes as it nears the extremity of the tail, 

 where the caudal marginal fin is slightly dentate. 



In the embryo of the anchovy, when it is ready to hatch, the gut is 

 ciliated in several parts (c, etc., fig. 19). 



In the larva of anchovy the pre-opercular apertures are widened, and 

 open into the pharynx. The wall of the oesophagus, which is narrow, is 

 very irregular. The lumen of the gut is slender; the walls are thick. 

 The anus opens at the middle of the width of the marginal fin on the 

 right side of the same. 



The gut in the larva of the whiting {Gadus merlangus) is shown in fig. 

 17. The rectum is constricted off from the intestine at con. A 

 peristaltic movement takes place in the rectum ; the movement begins at 

 the constriction and passes backwards in a wave motion. As the rectum 

 contracts the anus opens, and vice versa. Small rod-like bodies are seen 

 moving about in the rectum. The anus has three peculiar lobes. It 

 opens apparently in the space between the two leaves of the marginal fin. 

 From the anus grooves run out to the fin-margin, and they probably 

 indicate the position of a tube leading from the anus to the exterior {grv.^ 

 fig. 16). ^ 



Suh-epidermal Space. — Between the epiblast and the muscle segments 

 there is a comparatively wide space. The epiblast is a loose covering to 



