NOTES AND MEMORANDA. 155 



those who are prominently interested in and qualified to judge of the 

 subject. To secure the preliminary investigation and the moral power 

 necessary to this end, if the end is now attainable at all, they invite the 

 co-operation of the Societies as above mentioned, as well as of micro- 

 scopists generally. 



The questions are as follows : — 



(1) Is it expedient at present to adopt a standard for micro- 

 metry ? 



(2) If so, should the English or the metric system be employed ? 



(3) "What unit within the system selected is most eligible ? 



(4) What steps should be taken to obtain a suitable standard 

 measure of this unit ? 



(5) How can this standard micrometer be best preserved, and made 

 useful to all parties concerned ? * 



M. G. Huberson, the editor of ' Brebissonia,' thinks f it " is sad 

 that a second micrometric unit should be established in the New 

 World, when the Old World has already for a number of years adopted 

 the y^Vo o^ ^ millimetre as the unit of micrometric measurements, on 

 the proposition of Professor Suringar, of Leyden (Holland)." 



The Tomopteridae. — The interesting pelagic Chaetopods (" errant " 

 Annelides) which constitute the two genera of this family, have been 

 investigated by Gruber, Leukart, Carpenter, Claparede, and others. 

 Eecently, Dr. Franz Vejdovsky, of Prague, has taken up the subject, 

 and contributes a paper to Siebold and Kolliker's ' Zeitschrift,' | illus- 

 trated by two excellent plates, and dealing chiefly with certain points 

 in the anatomy of T, vitrina. 



1. Nervous System and Sense Organs. — There is a great amount of 

 discrepancy between the accounts of the central nervous system given 

 by different authors. Busch described a brain consisting of two united 

 ganglia, but saw no ventral nerve-cord ; the latter was described by 

 Gruber and by Kefertein, but Leukart and Pagenstecher saw only 

 the brain, and Carpenter and Claparede described in T. onisciformis a 

 single fibre passing from the latter along the dorsal side of the animal, 

 but denied the existence of the ventral cord and circumoesophageal 

 commissures. 



The nervous system of T. vitrina was investigated by Vejdovsky, 

 both in the fresh condition and after treatment with osmic acid, 

 alcohol, and picro-carmine. The brain is of a somewhat triangular 

 shape, the base being in front ; from its anterior angles the tentacular 

 nerves are given off, while from its ventral surface proceed the circum- 

 cesophageal commissures, which curve round the gullet, some of their 

 fibres uniting with one another in the middle ventral line, while others 

 are continued backwards into the ventral nerve-cords, a small interval 

 being left between the latter. In this interval lies a longitudinal row of 

 nerve-cells, while another row is situated immediately external to each 

 of the ventral cords, so that there are three distinct rows of nerve- 



* ' Amer. Jour, of Microscopy,' vol. iii. (1878) p. 279. 



t ' Brebissonia,' vol. i. (1878) p. 80. 



X 'Zeitsch. f. wiss. Zoologie,' vol. xsxi. (1878). 



