MORPHOLOGY. 
Odel, 7 
II. — MORPHOLOGY. 
Hydrozoa. 
The minute anatomy of the Hydroids has been submitted to careful 
examination by Zoja and Schneider. Zoja (84) by means of the methyl- 
blue method investigated more particularly the ultimate ramifications 
of the nervous system of Hydra , and is able to give figures of minute 
fibrils and nodules terminating in the ectoderm cells. 
Schneider’s paper (70) is very elaborate, and covers a wide field. The 
results of his investigations into the structure of the tissue elements are 
given in a series of figures. The minute anatomy of the ectoderm, endo- 
derm, mesogloea, muscle and nerve fibres, nematocysts, &c., is considered 
in detail. The genera used in his investigations were Carmarina and 
Pennaria, as representatives of the Hydro meduscr ; ForsJcalea , Apolemia , 
and Velella as representatives of the Siphonophora ; Pelagia of the 
Scyphozoa , and Alcyonium and Adamsia of the Anthozoa. 
Murbacii (60) has arrived at different conclusions to Schneider on the 
subject of the development of nematocysts. He states that the division 
of the nuclei of the interstitial cells, which form the nematocysts, is 
amitotic. A portion of the nuclear mass forms a little rod at the peri- 
phery of the cell, which soon passes into the substance of the cell. The 
rod then separates itself from the coll- protoplasm, excepting at one point, 
where it remains in contact with it. The rod then increases in size, and 
the thread is formed in a spiral manner round it. 
Chapeaux (25) says that physiological experiment teaches us that 
Hydra is a very sensitive animal, that the sensitivity is not localised m 
any particular region, but is distributed throughout the organism ; that 
the peristomatic region is the coordinating centre of movement, that the 
extremities of the tentacles are extremely sensitive, and that the cnidocil 
is an “Element sensoriel.” 
The cnidocil, he finds, is in connection with the nervous system, and 
the peristomatic region is morphologically the centre of the^ nervous 
system. 
Sigerfoos (72) states that, notwithstanding Lang’s investigations on 
the mode of gemmation of Hydra [ vide Zool. Rec. 1892], the blastostyle 
buds of Epenthesis are formed by evagiuation of both ectoderm and 
endoderm. 
Samassa (69), in a note on the origin of the sexual cells of the Cteno- 
phora , says that although it has not yet been actually proved, it is 
highly probable that they arise in Callianarid from the ectoderm. 
Nussbaum (64) observed that by changing some living Hydras from 
one tank to another, he was able to change their sex. His conclusions 
are that light, temperature, &c., have no influence in producing the 
change, but that it is entirely due to the amount of food present, a 
