D.—ZOOLOGY. 118 
in morphological work on nerve-elements is the investigation of the 
neuromotor system in the Protozoa. Sharp (1914), Yocom (1918), and 
Taylor (1920), working in Kofoid’s laboratory, have examined this 
mechanism in the ciliates Diplodinium and Euplotes and they describe 
and figure a mass—the neuromotorium—from which fibrils pass to the 
motor organs, to the sensory lip, and, in Diplodinium, to a ring round 
the cesophagus. The function of the apparatus is apparently not sup- 
porting or contractile, but conducting. By the application of the 
finest methods of micro-dissection specimens of Euplotes have been 
operated upon while they were observed under an oil-immersion objec- 
tive. Severance of the fibres destroyed co-ordination between the mem- 
branelles and the cirri, but other incisions of similar extent made 
without injuring the fibrillar apparatus did not impair co-ordination, 
and experiments on Paramecium by Rees (1922) have yielded similar 
results. While the experimental evidence is as yet less conclusive than 
the morphological, it supports the latter in the view that the fibrils have 
a conducting, co-ordinating function. Progress in our knowledge of 
the nervous system is but one of many lines of advance in our under- 
standing of the correlation and regulation of the component parts of 
the animal organism. 
The ciliate protozoa have been the subject during the last twenty 
years of a series of investigations of great interest, conducted with the 
purpose of ascertaining whether decline and death depend on inherent 
factors or on external conditions. While these researches have been 
in progress we have come to realise more fully that ciliates are by no 
means simple cells, and that some of them are organisms of highly 
complex structure. Twenty years ago Calkins succeeded in maintaining 
a strain of Paramecium for twenty-three months, during which there 
were 742 successive divisions or generations, but the strain, which had 
exhibited signs of depression at intervals of about three months, finally 
died out, apparently from exhaustion. From this work, and the pre- 
vious work of Maupas and Hertwig, the opinion became general that 
ciliates are able to pass through only a limited number of divisions, 
after which the animals weaken, become abnormal and die, and it was 
believed that the only way by which death could be averted was by a 
process of mating or conjugation involving an interchange of nuclear 
material between the two conjugants and resulting in a complete re- 
organisation of the nuclear apparatus. Jennings has shown that con- 
jugation is not necessarily beneficial, that the ex-conjugants vary greatly 
in vitality and reproductive power, and that in most cases the division 
rate is less than before conjugation. Woodruff has since May 1, 1907, 
kept under constant conditions in culture a race of Paramecium. 
During the sixteen years there have been some ten thousand generations, 
_ and there seems no likelihood of or reason for the death of the race so 
long as proper conditions are maintained. The’ possibility of conjuga- 
_ tion has been precluded by isolation of the products of division in the 
- main line of the culture, and the conclusion is justifiable that conjuga- 
tion is not necessary for the continued life of the organism. The 
criticism that Woodruff’s stock might be a non-conjugating race wag 
_ met by placing the Paramecia, left over from the direct line of culture 
K 2 
