REPORT ON THE PENNATULIBA. 31 



refractive particles, which completely conceal the outlines of the 

 endoderm cells. These particles, seen singh% appear of a pale 

 yellowish-brown colour ; but, in quantity, impart a deep brown or even 

 black colour to the endoderm of the stomach, which is very evident in 

 all the specimens. Conceruin<,' the use of these granules we have no 

 evidence whatever. They appear to be the same things described by 

 Gosse,* in Actinoloba, Tealia, Peachia, etc., as "a nearly uniform mass 

 of yellow fat-cells," and as hepatic in function. We much doubt the 

 correctness of either of these statements. It has been shown that in 

 allied forms these granules are insoluble in ether, and are therefore not 

 fat ; and concerning their supposed digestive functions, it must be noted 

 that they are confined to the endoderm cells, and never, so far as our 

 observations go, occur in either the mesoderm or ectoderm of the 

 stomach, so that they could only act on food not in the stomach, but 

 in the compartments of the body-cavity outside it, a position in which 

 it is very doubtful whether food is ever found. Moreover, we shall 

 find shortly that it is very doubtful whether digestion, at any 

 rate of animal matter, is really effected in the stomach at all, as 

 supposed by Gosse. And, finally, we would notice that the granules 

 in question are very closely similar to, if not indeed identical with, 

 the brown granules already described as occurring in the deeper parts 

 of the ectoderm cells of the body wall. 



e. The Mesenteries. — These are the eight vertical partitions or 

 septa which connect the stomach to the body-wall, and so divide the 

 body-cavity round the stomach into a series of compartments ; below 

 the stomach they extend, as previously noticed, to the bottom of the 

 body-cavity. 



Each mesentery consists (Figs. 10, 13, 16, and 15 o) of a thin central 

 mesodermal plate, clothed on each side by endoderm. 



The endoderm (ij) is very similar to, but slightly thinner than, 

 that lining the body-wall, with which it is directly continuous. It 

 consists of a single layer of short columnar cells, which contain, 

 especiall}' near the stomach, granules of the same character as those 

 just described in the endoderm of the stomach. 



The mesoderm is a thin connective tissue lamella, continuous on 

 the outer side with the mesoderm of the body- wall, and on the inner 

 side with that of the stomach. Between the connective tissue lamella 

 and the endoderm covering it, is a well-developed system of muscles, 

 the most powerful of which form the great retractor muscles of the 

 polype (Fig. 10 j)), by which the stomach can be drawn down, and the 

 tentacles pulled back within the calyx. 



Each retractor muscle, as shown in Fig. 10, extends the whole 

 length of the septum to which it belongs. Arising from the body- 

 wall, along the whole length of the base of attachment of the 

 septum, the fibres pass up in bundles in the substance of the septum. 



* Gosse : Op. cit., Introduction, p. xvii. 



