146 PART I. GENERAL ACCOUNT 



of light are lethal and they can only survive if sheltered from light. It goes 

 without saying that only intact animals can be kept alive — D.B.C.] 



Consistency, rigidity and elasticity vary enormously in the different forms, 

 and it is difficult therefore to indicate any method which might be suitable 

 for the extraction of all animals. Thick rigid tubes are sometimes compara- 

 tively easy to remove in bits by chipping or scratching away with a fine sharp 

 scalpel. In some small species, Siboglinum caulleryi for example, the tube can 

 be removed rather easily if it is torn lengthwise by means of a pair of mounted 

 needles. In many cases, however, it is not generally possible to extract the 

 animal from its tube without serious damage — for example, the delicate 

 Siboglinum minutum from its hard brittle tube, or the very soft Zenkevitchiana 

 longissima from its elastic easily torn tube. If, therefore, dissection cannot be 

 accomplished at one stroke, the pogonophore should be fixed in the tube. 

 A few species are generally easier to dissect after fixation when the body has 

 been hardened by alcohol. 



For the study of the very fine Siboglinum and Diplobrachia in particularly 

 stiff tubes, the material may first be soaked in diaphanol. After a few hours the 

 tube is so soft that it may easily be removed. At the same time it becomes 

 completely bleached and transparent, and one may study the external 

 morphology of the animal without removing it from the tube. It is necessary 

 to remember, however, that under diaphanol treatment the cuticular struc- 

 tures — the keels of the bridle, adhesive plaques and toothed bristles of the 

 girdles — are attacked and might be deformed. 



Animals still in the tube should be fixed in 70% alcohol only if the 

 consistency of the tube is sufficiently stiff. The alcohol should be changed 

 after 24 hr. Thin soft tubes of Siboglinum and the elastic tubes of Zenkevit- 

 chiana and other forms should be fixed in 2-3 per cent formaldehyde since 

 they shrink or become flattened in alcohol because of the rapid extraction of 

 water and the animal inside is grossly distorted. 



For histological fixation Bouin, Zenker, Helly or Stief may be recommen- 

 ded, or a saturated solution of mercuric chloride with acetic acid. These 

 fixatives should also be used for eggs and embryos, extracted from the tube 

 or still in a piece of it. 



The simplest fixative for neurohistology appears to be 4-10 per cent 

 neutral formaldehyde in which the material may be stored for up to three 

 months. 



For a complete systematic study we need not only the animal itself but its 

 tube too. The external morphology can be studied on fixed material under 

 the binocular or standard microscope, depending on the size. Measurements 



