650 SUMMAKY OF CUERENT RESEARCHES RELATING TO 



classificatory value, and are four orders of the class Turbellaria. 

 He enumerates in all twenty-one species, and expresses his opinion 

 that a considerable proportion will be found to be common to North 

 America and Europe ; into the interesting remarks that he makes on 

 already known species our space forbids ns to enter. 



Later Stages in the Development of Balanoglossus. * — Mr, W. 

 Bateson gives an account of his observations on the later develop- 

 mental stages of Balanoglossus KowalevsJcii, and makes a suggestion 

 as to the affinities of the Enteropneusta. A notice of Mr. Bateson's 

 work on the earlier stages of the species has been already given.f 



As the cilia of the larva disappear a peculiar organ, in the form of 

 a small papilla, bearing long cilia and mucous glands, appears on the 

 central part of the posterior surface ; this serves as a sucker, and then 

 entirely disappears ; it is essentially similar to the larval suckers of 

 Tunicates, Ganoids, and Amphibians, but it is not, apparently, an 

 ancestral character. 



Owing to the transparency of the body at an early stage the ali- 

 mentary canal may be easily seen to consist of an anterior branchial 

 tract, a middle digestive, and a posterior intestinal portion. As the 

 animal loses its cilia and before the second pair of gill-slits become 

 developed it creeps into the upper layer of mud, its mouth comes 

 to be directed forwards, a notochord becomes distinctly visible, and 

 the opercular fold appears in the form of a circular thickening. 



As the body increases in size it becomes more and more trans- 

 parent, but this phenomenon is, possibly, of no real significance, being 

 due merely to the rapid growth of the animal. As the body grows, 

 the number of gill-slits increases ; it seems probable that they go on 

 increasing during the greater part, if not the whole, of the life of the 

 animal ; the largest number of pairs of slits observed was fifty-seven. 

 As the gills appear in greater number the distinction between the 

 digestive and intestinal regions of the animal becomes better marked. 



Balanoglossus appears to have a very peculiar odour, which is 

 described by Mr. Bateson as being " very penetrating and persistent, 

 resembling that of chloride of lime with a foecal admixture." In a 

 new and as yet undescribed species — B. BrooJcsii — the smell, which 

 is strongly suggestive of iodoform, is very distinct after some months' 

 preservation in spirit (often changed), and is " a considerable draw- 

 back to investigating the species." 



There appears in the anterior dorsal wall of the gut, a most 

 remarkable structure which is regarded by Mr. Bateson as the noto- 

 chord ; it first arises by a forward growth of the anterior dorsal wall 

 of the pharynx, which thus shuts off a short diverticulum of hypo- 

 blast ; this is aided by a longitudinal constriction of the dorsal region 

 of the pharynx which gradually travels backwards, separating a hollow 

 hypoblastic tube, which remains open to the gut behind, and by a 

 forward growth from the point of junction with the gut. 



The skeletal rods first appear as two short rods of a deeply 

 stained, structureless substance which lie in the angles between the 



* Quart. Jouin. Micr. Sci. Supplement (1885) pp. 81-122. 

 t See this Journal, ante, p. 461. 



