THE ENTEEOPNEUSTA. 11 



due to thickening of the ectoderm and the appearance of 

 numerous mucous glands on the skin. The whole skin is 

 uniformly ciliated from the time when the blastopore closes 

 throughout life. 



At about seven to eight gill-slits the suctorial tail disappears, 

 probably atrophying rapidly, but as to this process nothing more 

 can be predicated. It is to be found in some larvae with eight 

 gill-slits, while others in the same stage are without it. The 

 anus is then terminal, circular, and permanently open. 



At ten gill-slits the ovaries are first perceptible, but as yet 

 are not marked enough to appear in a surface view. In older 

 animals they form large yellowish-grey projections from the 

 sides of the body. Their minute structure, together with that 

 of the testis, will be given later. 



The body of the adult is very highly coloured, the proboscis 

 being of a yellowish-white tint. The collar is a brilliant red 

 orange (especially in males), with a white line round the edge 

 of the operculum, while the rest of the body is of an orange 

 yellow, shading to pale green yellow in the intestinal region, 

 which is semi-transparent throughout life. The distinction 

 between the colour of the males and females is very well 

 marked in B. Kowalevskii, the genital regions being grey in 

 females and yellow in males. The sexes are of different colour 

 in all the Enteropneusta, most prominently so in B. sal- 

 mon eus (Giard), in which the males are chrome yellow and 

 the females salmon coloured. 



It may be well, before passing to the internal development, 

 to mention the peculiar odour which the creatures possess. 

 This odour is very penetrating and persistent, resembling that 

 of chloride of lime with a faecal admixture. All the species of 

 Enteropneusta which I have examined alive possess more or 

 less ofl'ensive odours. This peculiar property is most developed 

 in B. Brooksii (new species), in which the smell is very 

 distinct after the animals have been months in spirit, which 

 has been often changed. The smell of this species is strongly 

 suggestive of iodoform. It is so powerful as to be a con- 

 siderable drawback to investigating the species. 



