546 R. T. GUNTHER. 



Immediately to the outside of the mesogloea the great bulk 

 of tissue is chiefly composed of developing spermatozoa. As 

 in the spermarium of Oceaniaj described by O. and R. Hertwig 

 (1, p. 27), three different tissue zones may be distinguished. 

 Proceeding from within outwards (PI. 40, fig. 8), the first or 

 basal layer of ectoderm consists chiefly of large round nuclei 

 with but little protoplasm proportionately; secondly, there is 

 a thick layer of spermatozoa in various stages of development ; 

 and thirdly, there is an epithelial covering over all, the cells of 

 which send down processes in among the bundles of spermato- 

 zoa, and also seem to be in connection with long fusiform cells 

 penetrating between the spermatozoa in the second layer. 



In a single favorable section through the gonad of a male 

 Limnocodium of a certain degree of maturity all the various 

 stages of developing spermatozoa can be observed ; consequently 

 Limnocodium is a far more favorable object for the examination 

 of the process of spermatogenesis than the majority of 

 Hydroids, in which, as a rule, a complete series of stages of 

 developing spermatozoa are not found in the same gonophore. 

 In most Hydroids in which spermatogenesis has been studied 

 the developing spermatozoa of one gonophore all progress at 

 about the same rate, and so in a mature bud the younger 

 stages do not occur, and vice versa. In fact, it is of rare 

 occurrence that more than two different stages of developing 

 spermatozoa occur in the same bud. In Limnocodium, on the 

 contrary, all stages are often present. 



The following stages in the development of the spermatozoa 

 may be distinguished : 



1. The sperm mother-cells (PI. 40, fig. 8, a), situated next 

 the endoderm. These are characterised by their large nuclei, 

 which stain but slightly. They more or less correspond to the 

 Hertwigs' first layer in their description of the spermarium of 

 Oceania (1). Each of the nuclei of these cells has a well- 

 marked nucleolus. Eventually they divide by karyokinesis, 

 and give rise to — 



2. The daughter spermatoblasts (fig. 8, j3). The nuclei of 

 these cells are relatively much less than half the size of the 



