140 THE AMERICAN MONTHLY [August, 



A third peculiai-ity by which the sexes of the cray-fish can be distinguished 

 is the manner in which the female carries the eggs ; namely, in a mass upon 

 the 'swimmerets' or legs of the abdomen. This test of the sexes can, 

 however, be applied onlv when the females are spawning. These anatom- 

 ical details are equally true of the lobster. Anyone who cannot readily ob- 

 tain cray-fish can, perhaps, procure lobsters. These should always be bought 

 alive and killed with chloroform as directed above (see chapter i). It seems 

 hai'dly necessary to state that boiled lobsters would be of little value for his- 

 tological examination. The lobster does not present any advantages over 

 the cray-fish for histological study, nor is it inferior to the cray-fish ; choice 

 between them should be determined by the superior readiness of obtaining 

 either. It is not necessary to be particular with regard to sex in selecting 

 material for the preceding studies, because the liver, green gland, and in- 

 testine are alike in both males and females, as are all parts of the body except 

 the generative organs. Female specimen having been selected during the 

 breeding season, it is first killed by immersion in water into which a small 

 amount of chloroform has been previously dropped. After remaining in the 

 water a few minutes (5 or 10). the body may be opened by cutting oft' the 

 shell of the cephalothorax the large scoop-shape covering of the front part 

 of the body. Removal of this displays the stomach in the middle in front, 

 and the heart behind this ; in front of the heart, and on either side of the 

 stomach, the faint greenish yellow liver, composed plainl}^ of tubes, and un- 

 der the liver, on each side, the ovaries. These look brown in color, with 

 no greenish tint like the liver, and are composed of minute globules, giving 

 the organ an appearance like clusters of grapes. When found the ovaries 

 should be gently drawn away from the surrounding organs and prepared for 

 further examination, whether histological or anatomical. For anatomical 

 study the specimen should, as soon as it is opened, be placed in strong alco- 

 hol (75-90 per cent.) and dissected at once. For sectioning, the regular 

 course of hardening and imbedding should be pursued, or the egg may be 

 studied fresh from the ovary. Numeious methods of hardening are availa- 

 ble ; perhaps the one most convenient is by the use of corrosive sublimate 

 and acetic acid. The specimen from which the accompan3'ing plate has 

 been made and the present chapter written, was preserved, as described in 

 chapter i, for the green gland. It does well enough for our purpose. If the 

 corrosive sublimate method were chosen, immerse the perfectly fresh ovary 

 from a just-killed cray-fish (or lobster) in a mixture of saturated aqueous 

 solution of corrosive sublimate to which about i per cent, of glacial acetic 

 acid has been added. Leave the ovary in this solution about 15 minutes, 

 then remove to running water for two hours. From the water change the 

 specimen to 50 per cent, alcohol t hour, thence to 60 per cent, i hour, 

 thence to 70 per cent. 24 hours (at least). After several diurnal changes of 

 70 per cent, alcohol, the specimen may be kept in that indefinitely until it is 

 convenient to cut the sections. When such time comes, immerse in the stain, 

 wash and alcoholize, then imbed with paraffine or celloidin in the usual way. 

 In imbedding eggs by the method requiring the use of heat especial care 

 must be exercised. The bulk of substance of the egg of Cambartis is not 

 the ordinary protoplasm of animal cells, but a substance often called deutero • 

 plasm, or nutritive food yolk. It is well known as the ' yolk ' or • yelk ' of 

 the egg of birds. This substance often causes considerable difficulty to sec- 

 tioning because of its great hardness and brittleness in some cases. It both 

 dulls the razor and often lifts the edge slightly, so that the even thickness 

 of the section is interfered with. I have thought, without having especially 

 attended to the point, that my sections were better if I kept eggs in melted 

 paraffine of minimum temperature a minimum time. Some eggs of mol- 



