MORPHOLOGY. 13 



sides, and then appears to be coiled almost spirally around it. The upper end passes gradually 

 into the pedicle, while the lower extends as far as the beginning of the filament. In Praya 

 and Ilippojjoditis, this cord has a diameter of about j-o'soth of an inch, and differs in no 

 essential res])cct from the muscles in other parts of the body, especially in the stem, although 

 at times a slight transverse striation can be detected in it. In Dijj/ii/es, and still more in Abi/Ia, 

 however, this muscular cord becomes gradually thicker during its course, so as even to attain as 

 much as ~th of an inch in Mi/Ia, and therewith assumes a very distinct transverse striation, 

 so that, especially in Abi/Ia, it might be compared to the most beautiful transversely striped 

 muscular fibres. No nuclei can be observed in this cord, nor can its sheath be distinguished 

 from its contents. It appears as if the transverse striation were caused by a regular jointing, 

 for the edges of the cord are completely incurved at intervals, corresponding with the 

 constrictions between the joints. In Ahi/Ia, furthermore, this muscular filament is but 

 little flattened, and becomes triangular in many places by the mutual pressure of the 

 superimposed folds. If one of the thin edges be accidentally turned directly towards 

 the microscope, the transverse striation readily leads one to suppose that two series of 

 transverse rods are imbedded in the cord, as I indeed previously supposed to be the case." 

 (Z. N. K., p. 19.) 



I confess I entertain great doubts as to the real nature of this structure, which is 

 particularly worthy of the attention of future observers. 



In the tentacles of Stephanomia (PI. VII), which, in many respects, resemble those of 

 Halistemma, a new part makes its appearance, in the shape of a sort of hood, which 

 is developed at the junction of the pedicle with the sacculus, and encloses the latter like a 

 cup. I term this the involucrum. It is a solid, lamellar process of the ectoderm, containing no 

 internal cavity. The sacculus is very long and spirally coiled, terminates in a single filament, 

 and has a well-developed muscular band in its thin wall. 



In the genera Agalma and Athoryhia, the involucrum has become much larger in 

 proportion to the sacculus, and the latter is terminated, not by a single filament, but by 

 two filaments, between which the sacculus ends in a clear, thin-walled, median lobe, 

 devoid of thread-cells, and said to be contractile by Leuckart and KoUiker, though in the 

 species I observed it exhibited no such faculty (Pis. VI, IX). 



Finally, the tentacular branches attain their atraost complexity in Phi/sophora, the 

 spheroidal involucrum here completely investing the sacculus, which lies coiled up within it, 

 and having undergone other changes, which will be particularly described under the head of 

 that genus (PI. VIII). 



3. Hydrocysis. 



I apply this name to certain singular organs which are found more particularly in the 

 Physo2)Jiorida, and which resemble nothing so much as the imperfectly developed polypites of 

 the species to which they belong. As such, indeed, I always considered them, until 

 the perusal of the works of Philippi, Leuckart, and Kolliker, led me to modify my 

 opinion. 



These investigators term the organs in question " fiihler" and " taster," and are 



