400 Mr Willey, Some Zoological Results of a [Feb. 7, 



their length, in Pt. flava throughout their entire extent ; in other 

 words, the branchial sac is freely exposed to the surrounding 

 water. 



Observations made on living specimens of Pt. flava at the 

 Isle of Pines led me to suppose that this condition of the 

 branchial sac, with its skeletal supports, which include synapticula 

 or cross-rods, was more primitive than that in which the primary 

 bars are fused with the body-wall and the external openings of 

 the gill-slits are reduced to minute pores. This latter condition 

 would naturally tend to render the skeletal structures more or 

 less superfluous, and, in fact, as shown by Spengel, there are no 

 synapticula in Glandiceps and Balanoglossus. 



That this is a secondary loss rather than a primary deficiency 

 seems to me to be extremely probable, and this view is further 

 confirmed by the organisation of an Enteropneust which I have 

 described as a new genus, Spengelia 1 . This genus, apart from its 

 own peculiar features, exhibits close affinity to Glandiceps, but 

 it has synapticula. 



Another point which Spengel regarded as evidence of a 

 primitive nature was the absence of a circular layer of muscles 

 in the body wall of Balanoglossus. Spengel himself could not 

 avoid calling attention to the improbability of this defect in 

 the structure of a soft-bodied animal like Balanoglossus being 

 primitive, even while vindicating his position. In a species of 

 Ptychodera from Funafuti, recently described by J. P. Hill 2 as 

 Pt. hedleyi, Hill found that there was no circular layer of muscles 

 in the wall of the trunk-region, except at the extreme posterior 

 end, where it forms the anal sphincter. As this species belongs to 

 that section of the genus Ptychodera which bears most external 

 resemblance to Balanoglossus, there is obviously every reason to 

 suppose that the absence of circular muscles is also a secondary loss. 



Such considerations as the above are adduced for the purpose 

 of proving that Ptychodera {Ghlamydothorax) is the most primitive 

 and Balanoglossus the least primitive type of Enteropneusta. 



IV. Peripatus. Last year I obtained thirteen specimens of 

 a species of Peripatus in New Britain, which constitutes a new 

 (Melanesian) type equivalent to the types represented respectively 

 by the Neotropical, Australasian and Ethiopian species. In the 

 position of the generative orifice behind the last pair of legs it 

 resembles the Cape species, in the absence of crural glands it 

 resembles the New Zealand species, while the facts that the males 

 have a less number of claw-bearing legs than the females (22 pairs 

 in the former and 24 in the latter) and that embryos in all stages 



1 Q. J.M. S., Vol. xl. p. 623. 



2 Mem. Austral. Mus. in. Pt. 5. 1897. p. 335. 



