58 JOURNAL OF MARINE ZOOLOGY AND MICROSCOPY. 



regard to the compound forms, such as Botryllus, Aplidium, and the 

 like, where spirit results are notably so unsatisfactory. Comparative 

 retention of transparency with little or no shrinkage takes place 

 among even the most delicate, especially if a sea-water solution be 

 used. 



PISCES. Formalin is here again unmistakeably superior to 

 spirit, but as the former is somewhat inferior in penetrative power, 

 when its internal organs, viscera, brain, &c, are required for dis- 

 section, it is essential that these should be carefully exposed and 

 frequently moved during the first few days to ensure the fluid 

 having free access to the inner parts. When once stiffened, they 

 keep perfectly in a 4°/ or 5% solution, though even lower strengths 

 will ensure preservation. Such lower strengths are however not 

 advisable, for as the price of even a strong formalin solution is much 

 less than spirit, it would be folly to risk spoiling good specimens for 

 the sake of a few pence. 



Sponges, medusas, molluscs, tunicates and fishes are the groups 

 where the value of formalin reaches a maximum. 



COLOUR. Some writers have stated that formalin preserves most 

 colours unimpaired, but such an assertion can arise only from an 

 insufficient experience of its action. Lengthy familiarity has con- 

 vinced me that its extractive action in this respect is very similar to 

 that of spirit, and that the only difference is one of degree and not of 

 kind. Given a prolonged soaking in formalin, a red sea-weed or an 

 orange sponge will as surely fade as if they were in spirit, though if 

 kept out of strong light, the change may be so gradual as not to be 

 very noticeable for some time ; a weak solution, of course, takes 

 much longer to impair colour than a strong, and indeed if perfect 

 internal preservation be not an essential, the employment of a 2% 

 solution will not appreciably impair the colour for a fairly 

 considerable time. 



Where not stated otherwise in the preceding notes, a 5°/ 

 solution is to be inferred as the requisite strength. 



As indicating the comparative price of formalin as opposed to 

 spirit, I may mention that at present average prices, a 5°/ solution 

 should cost considerably less than half the price of spirit, and in this 

 connection it must further be borne in mind that in order to perfectly 

 preserve in spirit several changes are necessary — whereas in formalin, 

 except in rare cases, not even one change is needful— hence the cost 

 of a formalin solution ranges, in reality, from one quarter to one 

 third of that of spirit. 



