580 RECORD OF CURRENT RESEARCHES RELATING TO 



2. Histology. The fibres of the mesoderm, instead of being, as iu 

 Hydra, mere processes of the ectoderm cells, are independent spindle- 

 shaped muscular cells with nuclei. Tubularia has thus the most 

 differentiated mesoderm of all the hydroid polyps, the simplest con- 

 ditions being represented by Hydra, Syncoryne, and Podocoryne, while 

 Eydractinia affords an intermediate state, its muscle-fibres having 

 separate nuclei, but being in connection with the ectoderm cells. 

 There are two layers of muscular fibres in Tubularia, an inner longi- 

 tudinal layer, in contact with the gelatinous connective lamina, and 

 an outer transverse or circular layer. 



An account is given of the mode of formation of the thread-cells. 

 The cnidoblasts or smaller ectodermal cells in which these are formed, 

 are in direct continuity by means of fine protoplasmic processes with 

 the muscular fibres of the mesoderm. The thread-cells begin as a sort 

 of vacuoles in these cnidoblasts, in the neighbourhood of the nucleus, 

 but soon increase until they fill the cell. In all Hydrozoa yet 

 observed, the protoplasm of the cell is entirely absorbed j^C'^i passn 

 with the development of the thread-cell, but in Tubularia Ciamician 

 finds that a small portion of protoplasm surrounding the nucleus 

 becomes separated as a distinct cell, which may then itself give rise 

 to a new thread-cell. 



The connective lamina (Stiitzlamelle) which lies between the 

 muscular layer and the endoderm, can be isolated by long maceration 

 iu water and in ammoniacal solutions of carmine. The side turned 

 towards the mesoderm is seen to be smooth, while the inner side is 

 indented, the indentations corresponding to the large endoderm cells. 

 It is very resistent, about • 003 mm. thick, and shows no structure 

 under the highest powers. 



3. Ontogeny. The development of the gonophore is first con- 

 sidered, but little is added to the author's former paper,* except a 

 more exact account of the mode ui which the spadix breaks through 

 the distal wall of the gonophore, and a description of structures, in 

 the latter, which evidently represent the marginal tentacles of a 

 medusa. These occur in the form of eight elevations arranged in a 

 circle, at the distal end of the gonophore, around the projecting 

 spadix ; they are formed from the combined ectoderm and " medusoid 

 lamella " (the double layer of invagiuated endoderm) of the wall of 

 the gonophore. 



As in Hydra, only a few (four to eight) egg-cells in each gonophore 

 attain maturity, and become actual ova ; the remainder serve as food- 

 material for them. As in Hydra, also, sharply defined protoplasmic 

 spheres (pseudo-cells) appear amongst the clear yolk-spheres of the 

 egg, and these, Ciamician finds, multiply by a process of division, 

 which process, however, does not resemble these cell-divisions, but is 

 rather like a falling to pieces of the pseudo-cell. The egg is devoid 

 of a vitelline membrane. 



The interesting observation is made that some of the undeveloped 

 egg-cells may undergo division from true seminal cells. 



The process of yolk-division was actually followed in the living 

 * This Journal, ii. (1879) GG. 



