124 REPOKT ON THE PKNNATULIDA. 



Beneath the dermis is a well-developed system of longitudinal 

 muscles, arranged so as to form not a simple ring round the stalk, but 

 an extremely sinuous or corrugated one, the loops being very deep and 

 close together, and the total thickness of the layer about J that of the 

 entire wall. Within the layer of longitudinal muscles is a connective 

 tissue layer of varyiug thickness in different parts, and traversed by 

 ill-defiued bauds of muscular fibre whose geueral direction is parallel 

 to the surface of the stalk, though not forming a distinct system of 

 circular muscles. This layer forms also the basis of the septa or 

 partitions dividing the central canal. Finally, the central canals are 

 lined by a single layer of short columnar epithelial cells. 



The walls of the stalk are farther traversed by an irregular system 

 of canals or vessels of no great size, the largest of which have a longi- 

 tudinal direction and are situated in the loops formed by the layer of 

 longitudinal muscles. 



The lower third of the stalk differs materially in appearance from 

 the upper two-thirds. Its walls are softer and paler in colour, and 

 owing to the action of the spirit in which the specimens have been 

 preserved, are very distinctly wrinkled. This difference is due partly 

 to the wall of the lower third being somewhat thinner than that of 

 the upper part, but far more to the fact that in this portion the 

 dermis, which, owing to its calcareous spicules, is the most rigid layer 

 of the stalk, is barely half the thickness that it has above. 



We have described the stalk as seen in our spirit-preserved 

 specimens, but before leaving it a point of some interest remains to 

 be noticed. The stalk of Peimatula phosphorea is described and figured 

 by some writers as of very much greater thickness than we have 

 stated above, and is said to become inflated under certain circum- 

 stances or at certain times of the day. Thus Sir John Dalyell* 

 says that the whole Pen may distend itself with water, the 

 distension being most marked in the stalk. He remarks that " No one 

 could anticipate the effect of intumescence from its form in a con- 

 tracted state." Also, that " it enlarges remarkably as evening comes 

 on," Fennatula being, according to him, " strictly nocturnal," and, at 

 any rate in captivity, only expanding fully in the evening or at night. 



Johnstonf also notices that " when placed in a basin or plate of 

 sea-water, PennatuUc .... inflate the body until it becomes to 

 a considerable degree transparent, and only streaked with interrupted 

 lines of red." 



On the other hand, Panceri^, who has made cai'eful observations on 

 living PennatuUc, holds that this state of distension is not a natural 

 one. He says, " When these zoophytes, living at a depth of 40 or 100 



* Dalyell : " Bare and Remarkable Animals of Scotland," Vol. ii., 1848, pp. 191- 

 194, and Plate xllv. 



i Joluistou : " British Zoophytes," Second Edition, 1847, Vol. ii., pp. 160-161 ; 

 also, Figure 35, p. 158, where Pennatula jihospliorea is figured with the stalk thus 

 inflated. 



I Panceri ; '• Etudes sur la phosphorescence des animaux marins," Aiaiales 

 des Sciences Naturelles, Ciuquieuie Serie, tonje 16, lUTi, p. 15. 



