366 CALIFORNIA ACADEMY OF SCIENCES. [Proc. 3D Ser. 



far less extensive than with Stenostoma, and we do not 

 regard our negative results here as conclusive. 



We next selected for trial a species of Stenostoma, prob- 

 ably S. letLcofs O. Schm., which occurs in abundance at some 

 seasons of the year in Lake Merced and the Marine Hospital 

 Lake, San Francisco. This has proved favorable for our 

 purpose. After having found through a large number — 

 more than 150 — of preliminary experiments, the most 

 favorable conditions of temperature, food, etc., and the 

 best methods of keeping the animals that have been operated 

 on, we are now able to get positive results in nearly every 

 instance in which the proper conditions are fully met. 



The experiment in this case is very simple. The animal, 

 placed on a glass slide in a drop of water, is cut across with 

 a small scalpel, the operation being performed under a dis- 

 secting microscope. The slide with the drop of water con- 

 taining the animal is then kept in a moist chamber and 

 examined at short intervals as development proceeds. 



For some reason wholly unknown to us, the animals dis- 

 appear almost entirely during several months of the year, 

 i. e., from about July to January. Owing to this fact, we 

 have not yet been able to get a sufficient number of obser- 

 vations to clear up several subordinate but interesting points 

 that have arisen in course of the work. However, the 

 question which gave rise to the investigation having been 

 answered, we have felt that since it may be a considerable 

 time yet before we shall be in position to publish our full 

 results, a brief presentation of the main point is desirable at 

 the present time. 



3. General, Statement of Result. 



Stated in a word, the answer to the initial question is this: 

 Under certain conditions artificial section of a dividing 

 zuoj'ni, in another -plane than that of normal fission, inhibits 

 the normal fission -plane and transfers to the artificial plane 

 the production of those structures of the derivative worm 

 that would otherwise have been produced adjacent to the 

 normal fission plane. 



