DERMAL SYSTEM. 13 



A peculiar condition of the endocyst of Lophopus, though most probably only abnormal, 

 must be mentioned here. In specimens of this Polyzoon which had been kept for a few days, 

 and occasionally in some just captured, multitudes of minute oval brilliant corpuscles were 

 seen to have been developed in the endocyst throughout its whole extent. They were not 

 scattered at random through this membrane, but were contained in the interior of a system of 

 tubes which formed a network in the substance of the endocyst (PI. II, fig. 13). They are 

 about the ^^\ of an inch in the longer diameter, larger at one end than at the other, and 

 in the large end they appear to contain a minute cavity (fig. 14), which under the action of 

 acetic acid dilates and fills nearly the entire corpuscle (fig. 15). The situation of these bodies 

 in a tubular network in the substance of the endocyst is a fact of great interest. It is nearly 

 certain that whatever may have been the origin of the corpuscles, they found the tubes already 

 existing for their reception. It would follow from this that the presence of a reticulated 

 system of tubes in the substance of the endocyst is the normal condition of this tunic, but 

 from the delicacy of these tubes, and the transparency and want of colour of their contents, 

 they escape detection under ordinary circumstances, and are first revealed only by the abnor- 

 mal (?) development of the peculiar corpuscles in their interior. These corpuscles are not 

 confined to the endocyst, but are also found at the same time in other tissues, especially in 

 the substance of the funiculus, which, as will be afterwards shown, connects the fundus of 

 the stomach with the walls of the cells. In the endocyst alone, however, do they appear to 

 be contained in distinct canals. 



In CristateUa, where the endocyst constitutes the whole of the coencecium, it presents 

 below a flattened disc, which closely resembles the foot of a gasteropodous mollusc, and on 

 which this singular colony creeps about on the stems and leaves of aquatic plants, exposing 

 its beautiful plumes to the light and warmth of the sun (PI. I, fig. 2). 



The edocyst or external investment (PI. Ill, fig. 7 , V, figs. 5, 6 ; IX, fig. 7 ; X, fig. 4, a) 

 is, in most of the species, composed of a tough pregamentaceous brown membrane, strength- 

 ened by the deposition of irregularly formed siliceous and other earthy particles, which, except 

 towards the orifices, where these particles are deficient, give to the ectocyst an opacity which 

 renders an observation of the contained parts a matter of considerable difficulty. In some 

 species of Plumatella, and in Alci/oneUa flabellum and A. Benedeni, the earthy particles are 

 entirely absent, from a longitudinal line which commences wide near the aperture of the 

 cell, and gradually narrows as it passes backwards, when it soon assumes the appearance of a 

 prominent keel, and then loses its transparency by the deposition of earthy matter, as in the 

 rest of the ectocyst (PI. VIII, figs. 2, 3). The perfectly transparent wide origin of this line 

 gives to the orifice of the cell the appearance of having a deep notch on one side. In Frede- 

 ricella a slightly prominent keel is also apparent, but the notch-like transparent space does 

 not here exist. 



In CrisfafeUa (PI. I) the ectocyst would seem to be entirely absent ; and this genus, 

 therefore, presents the anomalous condition of having the ccenoecium composed exclusively 

 of the endocyst.* 



* Thi.s view of tlie coencecium of Crisiatel/a is contrary to the opinion previou.sl}' expressed by me, 

 but I am now convinced tbat wliat I formerly described as the ectocyst of CristafcUa is really the 

 endocvst. 



