8 BASIC METHODS FOR EXPERIMENTS 



Whenever this Is not possible, the experimental embryologist 

 should think twice before he undertakes laboratory work on 

 the egg — especially if he can not procure a sufficient number of 

 stages from natural surroundings with which to compare those 

 that he obtains in the laboratory. The forms whose eggs I 

 treat in this book have been studied in nature. The literature 

 on them thus furnishes a guide as to their peculiar habitat, 

 geographical and seasonal distribution, breeding habits, etc. — 

 a guide which introduces the experimenter more quickly to 

 the flavor of natural history, the pleasurable appetizer of bio- 

 logical work. 



To be sure there are numerous instances on record that attest 

 the fact that life-histories of animals have been ascertained only 

 through observations in the laboratory: those of many nereids, 

 of species of syllids, etc., phases of which were first described 

 as distinct species. Also, are there forms, as for example, 

 Balanoglossus, whose early life-histories up to now we know only 

 as they run in the laboratory. These instances do not minimize 

 the value of my point, namely, that the experimental embryolo- 

 gist should as far as possible know his animal personally and 

 directly through work in the field, never resting content to 

 become what Kropotkin in another sense denominated a 

 "desk-biologist." 



In most cases it is not an insurmountable task for the worker 

 to collect his own animals. Indeed, he must often collect them 

 himself because the sensitive nature of some animals demands 

 extreme care in handling after capture and the greatest expedi- 

 tion in transport from collecting grounds to the laboratory. If 

 one wishes to observe the fertilization-reaction in the egg of 

 Jmphioxus, one would best do this immediately upon capture 

 of the animals because it is difficult to obtain shedding animals 

 in the laboratory. Lwoff's old observation on this point I was 

 fortunate enough to repeat in Naples. (Lwoff, 1892; Just, 

 1939; see also Orton, 1913-1915.) In the region of Roscoff, 

 Echinocardium caudatum is extremely abundant but the animals 

 even with greatest care are injured during transport to the 

 laboratory. At Woods Hole, Echinarachnius if not properly 

 cared for after having been dredged soon deteriorates. One 

 may readily recognize deterioration in this animal because its 



