214 



Part III. — Sixteenth Annual Report 



The gut (g.) appears in the embryo of Tracliinus vipera]\x?>t after the 

 closure of the blastopore, at which stage the cardiac swelHng alone 

 indicates the position of the future heart (fig. 23). It is a narrow tube 

 with delicate walls ; its anterior end stops short of the pectoral region, and 

 it extends posteriorly to the end of the tail. In its middle portion the 

 gut widens considerably. Its hind extremity is somewhat obscured by 

 the thick mass of loose tissue at the end of the tail, but it appears to open 

 out in a funnel-shaped aperture. In the egg of Sen-anus hepatus, before 

 the hefirt begins to pulsate, at a stage when the tail reaches a little beyond 

 the yolk, the gut is not well defined and appears to have minute lateral 

 branches. In the egg of the anchovy {Engraulis encrasicliolus) also the 

 spaces between the muscle segments resemble line canals and appear to be 

 connected with the gut. A communication by means of these canals 

 between the gut and the subepiblastic space probably exists. In the egg 

 of the anchovy when the blastopore closes there is no trace of the gut. 

 There is a distinct longitudinal space lying below the neurochord, bounded 

 laterally by the ventral halves of the muscle segments, and ventrally by 

 the hypoblast (ns., fig. 22). This space appears to be filled with a homo- 

 geneous fluid in which there is no trace of cells. In an egg measuring 

 •94 mro. (and having an oil globule '19 mm. in diameter), in which the 

 tail of the embryo was just appearing above the yolk, such a subnotochordal 

 space >vas well seen. In the same egg, at a little later stage — but before 

 the cardiac swelling had appeared — the gut was already formed. In the 

 egg of Species No. 3 (Raffaele),* when the blastopore closes there is no 

 trace of the gut. 



The next stage in the development of the gut is marked by the forward 

 extension of the gut and the appearance of the two ^' pre-opercular 

 apertures" {p.o.a.), one on each side. The pre-opercular apertures oj^enby 

 furmehshaped mouths to Wxq perivitelline space ; from each aperture (p.o.a.) 

 a canal runs to the middle line of the embryo and joins the anterior end 

 of the gut (fig. 21) ; the apertures are situated immediately ventral to the 

 ear capsules. The heart is not yet formed. The anterior portion of the 

 gut is now ciliated (c, fig. 21). The cilia vibrate from before backwards, 

 thus causing a current to enter from the perivitelline space by the pre- 

 opercular apertures and to pass posteriorly along the gut. The fluid in 

 the perivitelline space — which differs from sea water only in possessing 

 certain minute corpuscles — thus passes through the gut to find exit in the 

 loose tissue of the tail. Outside each pre-opercular aperture there are 

 the so-called ^'pectoral filaments" ; these (p.f.) are simply tinger-like 

 grooves uniting at the mouth of the pre-opercular aperture (figs. 9, 21, 

 and 20). A few corpuscles are seen at the ends of the filaments. 



In tlie egg of Serranus hepatus^ at the stage when the heart commences 

 to pulsate, the gut has very irregular walls. The extremity of the tail 

 has the appearance of being broken up into a number of canals. The gut 

 is continued anteriorly as far as the front end of the notochord by a canal 

 of the same width as itself. The cilia are vibrating actively in the 

 sesophageal portion of the gut. In the egg of anchovy also, when the tail 

 of the embryo projects a little beyond the yolk, an anterior continuation 

 of the gut to the head exists. 



The cilia in the gut do not act continuously, but intermittently ; it is 

 only at the moment when they are actively vibrating that it is possible to 

 make them out. 



In the egg of Trachinus vipera, when the embryo is two-thirds de- 

 veloped, an anterior continuation of the gut is seen. This anterior canal 

 divides into two branches — one of which proceeds to a pore on the dorsal 



♦ I. c. 



