REPORT ON PHORONIS BUSKII. 7 



bladder-liko part often occurs — marked by a close series of longitudinal bands — 

 as well as crossed externally by fine transverse striae, so that the region has a tessellated 

 appearance. Such an aspect, of course, diverges very much from the eight longitudinal 

 bands in Edwardsia and Cerianthus, though, as will afterwards be noticed, there is a 

 certain structural resemblance between the muscles of the diverse groups. Even in 

 the somewhat narrower region of Phoronis, behind the latter part, traces of these 

 longitudinal bands (the muscular fasciculi) are visible. These are much more distinct 

 than in the smaller species, — though in the latter they were at once recognised and 

 well figured by Professor AUman in his remarks on Phoronis hipjyocrepia in the 

 Fresh-Water Polyzoa. Finally, the body ends in a more or less clavate or bulbous 

 region, which is generally devoid of such markings. 



Body- Wall. 



a. Cttticle mid Hypoderm. 



b. Basement-Tissue. 



c. Muscular System. 



Cuticle and Hyj^oderm. — The contracted anterior region of the body, after its 

 special muscles are fully formed (PI. I. fig. 3),' presents externally in transverse 

 section the delicate cuticula which envelopes the entire animal with the exception 

 apparently of certain parts of its branchial system. The hj^poderm {hp) underneath 

 — even in fine sections of this region — is almost opaque from the deposit of blackish 

 pigment. This layer seems to have the same intimate structure as in the Annelids ami 

 Nemerteans, viz. an areolar stroma with gland-cells and granules. In transverse section 

 it is somewhat regularly and closely streaked vertically. In longitudinal sections, 

 again, it is thrown into a series of closely arranged ridges — each composed of a central 

 area and a somewhat radiate or foliate arrano-ement of mars;inal cells. This condition 

 is doubtless due to the very elastic nature of the subjacent basement-tissue, which 

 adapts itself more readily to the muscular contractions, while the less facile hypoderm 

 is thrown into numerous wrinkles. In the j^osterior or dilated region the hypodermic 

 tissue is somewhat more areolar and lax ; and in young specimens it is proportionally 

 thicker all over than in the adults. In those in which the peculiar posterior gland 

 with its external channel is well developed, the hypoderm of the region is massive. 

 This coat, then, is uniformly on a much larger scale than in the smaller Australian or 

 the ordinary European species, and conforms to the type seen in the Annelids and 

 Nemerteans rather than to anything known in the Gephyrea or Polyzoa. 



Basement-Tissue. — Beneath the foregoing is a translucent and highly elastic 



^ I am indebted to Mr. Jolin Wilson, Demonstrator of Zoology and Lecturer on Botany in the University of St. 

 Andrews, for his kind aid in making sections of Phoronis, and, along with Mr. E. E. Prince, for valued assistance in 

 drawing some of the figures. 



