ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 



835 



tion. To effect this two methods are in vogue ; the one acts with rapidity- 

 sufficient to prevent contraction, the other kills slowly by means of some 

 piiralysing medium. Absolute alcohol, osmic acid, sublimate solution, 

 chromic acid, and other mineral acids are agents of the rapid process. 



Paialysis is produced by slow cooling, or gradual warming, or even by- 

 immersion in boiling water ; but good service is rendered by alcohol 

 chloroform in watery solution or vapour, sulphuric ether, prussic acid, 

 carbonic acid, atropin, nicotin, strychnin, chloral hydrate, cocain. As 

 suitable reagents for some of the divisions of the Invertebrata, the follow- 

 ing are recommended. : — 



BMzopoda. —For rapid fixation, osmic acid, and after-treatment with 

 picrocarmin, or absolute alcohol, sublimate, and chromic acid. Chinin in 

 weak solution produces palsy of the protoplasm. 



I Infusoria. — For j)aralysing ciliary action, chloroform, soda or seltzer 

 water. For killing quickly, osmic acid, sublimate, absolute alcohol, or 

 chloral hydrate. Keeping animals alive but paralysed, salt solution, 

 liegulated compression under cover-glass for purposes of observation 

 effected by melting away wax supports with heated needles. 



Spongia and Ccelenterata. — For sponges no reliable method is known. 

 For Hydromedusa, Scyphomedusa, and Ctonophora, the rapid action of 

 osmic acid. At Naples, polyps are killed rapidly with success by a boiling 

 mixture of equal parts of sublimate and acetic acid. With Siphonophora, 

 paralysing with chloral hydrate is excellent. For Pennatulida with large 

 polyps the gradual addition of fresh water. For histological work, 

 Anthozoa may be paralysed with chloral, but this, like cocain, sometimes 

 gives rise to contraction and. deformity. For museum specimens, Anthozoa 

 should be killed suddenly as with glacial acetic acid. 



Echinodermata. — Casting of the arms may be avoided by imbedding 

 star-fish in sand. The colour of star-fishes may be retained by immersing 

 them for about 6 hours in Wickersheimer's solution. 



Worms. — Some alcohol poured on the surface of the water in which the 

 worms are, or chloroform water, acts as a paralysing agent. Warm solution 

 of corrosive sublimate or picro-sulphuric acid. Nemertines remain 

 extended in chloral hydrate, yet much depends on the degree of concentra- 

 tion of the paralysing fluid. Sudden heating over the flame of a spirit- 

 lamp kills Trematoda. For Polychteta, alcohol. It is very difficult to 

 obtain Eotifera in the extended condition. Carbonic acid water, chloral 

 hydrate, cocain, followed by hardening in osmic acid or cocain solution 

 cooled in ice, all recommended. On Bryozoa the last named medium 

 has the same effect; chloral is not always satisfactory for the marine 

 forms. 



Mollusca. — Hot water for fixation. For slugs, tobacco smoke or con- 

 centrated sublimate may be used. Chromic acid should be altogether 

 avoided as it renders them too brittle. 



Tunicata. — Large animals are killed by passing a glass tube into the 

 two openings and then injecting glacial acetic acid, alcohol, or Kleinen- 

 berg's fluid. Small species may be killed by pouring some alcohol or 

 Kleinenberg's fluid and spirit on the top of the water. 



Influence of reagents on the Fertilization and Segmentation of the 

 Animal Ovum.* — Drs. O. and E. Hertwig who have previously demon- 

 strated that the ova of the sea-urchin became weakened by immersion in 

 sea water, and therefore became more susceptible to hybridization or poly- 

 spermia, i. e. to the penetration of several spermatozoa, now discuss the 



* Jenaische Zeitschr. f. Naturwiss., xx. (1887) pp. 120-4 (7 pis.). 



