156 Marine Investigations in South Africa. Vol. V. 



therefore elongated, or broadened upwards towards the tentacles 

 here, and, in the same region, elongated downwards in the lateral 

 folds. This downward elongation comes in close approximation 

 to the nephridia, as shown in fig. 5, which is a transverse section 

 of specimen A. 



With regard to the interpretation of this organ, the most obvious 

 suggestion is that it is of the nature of an introvert, such as occurs in 

 the Polyzoa and Sipunculoidea, and, if so, it might form another link 

 between the Phoronidea and these groups. It seems probable from 

 its size, structure, apparent absence of retractor muscles, and intimate 

 relation with nerve ring, that it does not however act, to any great 

 extent at least, as an organ for the withdrawal of the body, or any 

 part of it — a function which is most efficiently performed by the 

 numerous and powerful muscles of the body. 



In specimen A we are dealing with a regenerated head, not 

 impossibly in B also, and it n,iight be suggested that the fold is a 

 stage in the complete separation of the nerve ring from the epi- 

 dermis — a condition which might occur in a completely developed 

 specimen, though the nature of the folding does not seem to sup- 

 port such a view. 



If any phylogenetic significance is to be attached to the form 

 of this organ, which is possible, it may be that it is the remnant 

 of an ancestral introvert which has been retained with the new 

 function of protection of the nerve ring. 



Muscles. — The longitudinal muscles of the body were numerous 

 and well developed, especially on the left side. In the region just 

 below the nephridia there were 32 in the left oral chamber, 30 in the 

 right, 18 in the left anal chamber, and 14 in the right, or, according 

 to Longchamps' formula, ^yj^|. 



Lophophoral Organ. — In specimen A this organ was not present 

 but in specimen B it was very marked, being a deeply staining 

 mass of glandular cells. 



Tentacles. — The tentacles were numerous — 126 in specimen A. 

 They were a little over 3 mm. in length, and -08 mm. in diameter. 



Septa. — The septa seemed to be of the usual number and 

 disposition. The transverse septum was in part without basement 

 tissue. In median longitudinal sections there appeared an off- 

 shoot towards the epistome — a condition which requires further 

 examination and confirmation on other specimens. 



Nephridia. — The two nephridial tubes are well developed, and in 

 preserved material were bent on themselves, forming a loop, the 

 limbs of which appeared of about equal length. As described above, 

 the nephridial tube of the left side passes between the nerve and the 



