ch. xi PEACTICAL HINTS 559 



Amphioxus becomes inconvenienced by such entangled eggs amongst 

 the cirri it is able suddenly to reverse the respiratory current so as to 

 clear them away, and in this way there is produced a misleading 

 appearance as if the eggs were being laid through the mouth. The 

 first meiotic division has been completed before oviposition while the 

 second is in the spindle stage at this period. Fertilization probably 

 takes place immediately, spermatozoa being disseminated through the 

 water. 



It is best (Cerfontaine, 1906-7) to bring the adults into the 

 laboratory and wait until they spawn which operation may be 

 considerably delayed. To a dish of pure sea-water is added a little 

 sea-water containing sperm then the eggs, collected with a pipette as 

 soon as extruded, are added. 



Batches of eggs are fixed periodically, preferably in strong 

 Flemming's solution or Hermann's solution. After dehydration they 

 are placed in a mixture of 2 parts clove oil and 1 part collodion 

 in which they may be kept indefinitely. For examination whole the 

 egg or embryo is placed on a slide or coverslip in a drop of the 

 clove-oil-collodion. After the specimen has been arranged in the 

 desired position by means of needles a drop of chloroform is applied 

 in order to cause the collodion to solidify. The whole is then cleared 

 with cedar oil and mounted in Canada balsam. For the preparation 

 of sections the procedure is similar, only in this case the slide or 

 coverslip should be coated with paraffin as a preliminary to allow 

 the collodion block to become detached, and the latter should be 

 embedded in paraffin. 



Petromyzon. — The various species of Lamprey make their way up 

 streams to suitable gravelly spots for spawning in the spring or 

 early summer (April, May, in the northern hemisphere). Material 

 for embryological study is best got by " stripping " the ripe males and 

 females i.e. by passing the hand back along the body with gentle 

 pressure so as to force out the eggs or sperm. The gametes from the 

 male and female are collected separately in two small dishes : they 

 are then mixed together, stirred gently with a feather, and water 

 added. This " dry " method gives a smaller proportion of unfertilized 

 eggs than when the eggs are received from the fish directly into 

 water (Herfort, 1901). As fixing agent the ordinary corrosive 

 sublimate and acetic acid is quite satisfactory. 



Myxinoids. — The only Myxinoid eggs that have been obtained 

 in any numbers are those of Bdellostoma which are dredged near 

 Monterey, California, on shelly and gravelly bottom at a mean depth 

 .of about 12 fathoms (Bashford Dean, 1899). Much still remains to 

 be done in working out the details of their development but it is 

 clear that this is of a highly peculiar and specialized type. 



Elasmobranchii. — The eggs are fertilized in the upper part of the 

 oviduct. They may traverse the oviduct comparatively rapidly and be 

 laid as in Birds at an early stage of development [Chimaera, Scylliidae, 

 Cestracion, RaicC] or they may remain in the oviduct for a prolonged 



