ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 463 



contrary its changes are manifold. Nor, again, are the spermatoblasts 

 multinucleate. 



Spermatogenesis in the hydroids examined by the author presented 

 the following history : the primary spermatoblasts, which had been 

 diflferentiated from the primitive germ-cells, and which were distin- 

 guished by their rich supply of protoplasm and sharply contoured 

 nuclei, for a time increased in number, but not in size. When the 

 latter did occur it was at first only gradual ; the richness in proto- 

 plasm became less well marked, and the nuclei increased in propor- 

 tionate size, so that a matured testis seemed to be filled with nuclei. 

 Later on a change in the nature of the spermatoblasts was indicated 

 by the difference in effect of staining fluids on the nuclei, the nucleoli 

 of which were now completely hidden ; in fact, the nuclei appeared to 

 be quite homogeneous. As the nuclei changed the protoplasm of the 

 germinal cell lost its power of taking up staining fluids. It is pos- 

 sible that these two changes are in causal connection with one 

 another, substances from the protoplasm passing into the nucleus. 



The cells nest divide into spermatoblasts, the nuclei of which 

 become the head, and the protoplasm the elongated tail of the sperma- 

 tozoa ; the head is ordinarily highly refractive ; the head itself varies 

 in form in various species, but in all cases the nuclear division is 

 effected in an indirect manner. 



The testicular mass is extraordinarily large in hydroids which 

 have sessile gonophors, and the number of spermatozoa is consequently 

 very large ; it is not difficult to correlate this with the fact that the 

 producing mass remains fixed, for a number of spermatozoa must be 

 lost in the water without effecting their function ; most hydroid stocks 

 are dioecious, or, in other words, male and female products are by no 

 means in close proximity. The spermatozoa and even the spermato- 

 blasts are definitely arranged, either in chains, bands, or groups. 

 The heads appear most often turned towards the periphery, but in 

 Sertularella they are grouped around the meshes of a stroma ; this, 

 which is of ectodermal or endodermal origin according to the structure 

 and position of the testis, appears to be widely distributed, though not 

 always so well developed as in Sertularella. The presence of stinging 

 cells in the testis of Clava is confirmed. 



The author expects that studies on spermatogenesis in Medusoid 

 forms will show that the history of development is in them very similar 

 to what he has shown to obtain in hydroid forms. 



Histology of Porpita mediterranea.* — M. M. Bedot, who has 

 already studied the VelellidBe,"!" finds that, as in them, the Porpitidae 

 have the organ (central organ) which is ordinarily known as the liver, 

 formed of a number of canals and of a large mass of cnidoblasts ; the 

 canals differ in structure in different parts, and are not the same as in 

 the Velellidge, for their cells are closely packed. The prominent 

 bodies which are amorphous in Yelella are replaced by well-marked 

 granules and by crystals of bright green colour (guanin) in Porpita. 



* Rec. Zool. Suisse, ii. (1885) pp. 189-94. 

 t See this Journal, iv. (1884) p. 576. 



