10 THE VOYAGE OF H.M.S. CHALLENGER. 



general mass is composed of smaller fibres in somewhat pinnate rows, the central region 

 having a larger amount of translucent myolemma (PI. I. fig. 5). Moreover, between 

 each ovate mass a smaller bundle of longitudinal fibres exists, the tip apparently being 

 prolonged into the radiate strands which occupy the usual position. In the succeeding 

 part of the body the muscular layers diminish in proportionate bulk, and towards the 

 posterior end the pennate arrangement of the longitudinal fibres disappears, and they 

 form a comparatively thin layer under the basement-tissue, the circular fibres being 

 internal. The arrangement of these longitudinal fibres in this region is peculiar — little 

 spaces or lacunae often appearing on their inner aspect (PL I. fig. 6). Terminally again 

 they form a closely interwoven series, as shown in PL III. fig. 4, dm. 



It is interesting to note the gradations existing between the lax pinnate arrange- 

 ment of the longitudinal muscular bands in Pcnchia, the somewhat coarse pennate 

 system in Phoronis, and the more finished plan of the muscles in the Eriographididse. 



In young examples the radiate muscles anteriorly are more perfectly seen than in 

 the adult, and they fill up the body-cavity of the region to a considerable extent. 



Strethill Wright was of opinion that the muscular system of Phoronis consists of a 

 layer of flat longitudinal bands immediately beneath the integument, while within these 

 a series of fine circular fibres could with difficulty be traced. He had thus probably 

 misinterpreted the arrangement in optical section. Schneider, again, observes that 

 the larval sac (which becomes the elongated " body " of the adult) before extrusion 

 shows a cellular layer with nuclei, then a longitudinal coat and apparently a few small 

 cells, followed by a transverse or circular layer. The inner coat, the future epidermis, 

 was indistinct. Kowalewsky mentions under the epithelial layer of the body a circular 

 coat, and an inner layer of longitudinal muscular fibres — a structure which corresponds 

 generally with the typical condition. 



A feature of considerable importance in the group is the presence of a peculiar 

 glandular apparatus, seen in section in PL II. figs. 3-5, communicating with the 

 exterior by a definite channel with well-formed walls. This structure lies quite beliind 

 the alimentary system as well as the mesenterial sej^ta. Anteriorly it seems to end in 

 a mass of tissue having no very definite environment in some of the preparations, and 

 apparently having a granular glandular structure, the greater part of the area being 

 coarsely granular, with numerous opaque bodies like folds or wrinkles towards the centre 

 of the mass. In others, again, it leads to the posterior end of the reproductive organs. 

 As we proceed backward, this peculiar streaked glandular region is differentiated from 

 an outer and somewhat coarsely granular layer. The inner region then presents larger 

 gland-cells with nuclei and granules, and the wall becomes more definite. In the 

 condition shown in PL II. fig. 3, the outer surface is covered with the granular mass 

 (probably consisting of the perivisceral corpuscles and endothelium) which is found coating 

 the inner surface of the body-wall. Beneath are some definite circular fibres, then a 



