144 BULLETIN OF THE 



E. L. Mark, a more particular consideration of some moot anatomical 

 and histological points was undertaken. This was unfortunately limited 

 by the material on hand, which consisted merely of the anterior portion 

 of the body, corresponding in general to the introvert of recent writers. 

 As this contains, however, nearly all of the important organs of the 

 nervous system to which especial attention has been paid in this paper, 

 and as its separation from the rest of the body at the time of killing 

 insured good preservation, it is hoped that the conclusions reached may 

 not be without value, in spite of their incompleteness. The histological 

 structure of the body wall and of the nervous system has been treated 

 in detail, and from the results an attempt has been made to throw some 

 new light on the systematic position of the Sipunculids. 



Methods. 



The material used in these investigations was preserved with especial 

 care, and every effort was made to procure a method of killing which 

 should afford a clear idea of anatomical and histological relations under 

 normal conditions, since many of the contradictory statements of va- 

 rious writers have been undoubtedly the result of studying specimens 

 in a distorted state, due to muscular contraction, or have followed 

 the examination of tissues poorly preserved. The thick impermeable 

 cuticula, and the wealth of muscular tissue in the body wall, render it a 

 difficult matter to avoid at the same time both evils. The method 

 finally adopted as yielding the best results is as follows. 



After remaining some time in clean sea-water to clear tentacles, body 

 wall, and oesophagus of adhering sand, the animals were brought into 

 a shallow dish of sea-water, and 5of alcohol was allowed to flow gently 

 over the surface, forming thus a thin film, which disseminated itself 

 gradually, and produced in the animals a complete relaxation of the 

 body muscles. It did not seem to answer equally well when the alcohol 

 and water were mixed at the start, as has been recommended for some 

 animals. The length of time necessary for the attainment of com- 

 plete narcosis cannot be exactly given. It varies greatly with different 

 individuals ; but if, after lying some four to eight hours, the animals make 

 no contractions on being gently probed with a dull instrument, they may 

 be regarded as sufficiently stupefied, and transferred to 50^, alcohol. 

 After a short stay in this, the introvert was cut off, and this alone sub- 

 jected to treatment with higher grades of alcohol, which insured the pene- 

 tration and consequent good preservation of the tissues. The only point 

 in the process which requires especial care, and which often produces 



