1002 ELLIOT ROWLAND DOWNING 
Thérgametozoon!a 2x forays is scent tpt oo dh vans Ae oe et oe eee 1037 
/thercommonsplant andianimall prototypes ene eaten 1037 
The primitive position of the reduction phenomenon....................... 1038 
Its shift toward typical plant and animal positions..................... 1038 
Reduction and, tetrad formations+ < 25. c.4222% .,. 8.056 ieee Oe ee 1039 
Beard’s hypothesis of alternation of generations in animals................. 1039 
BUTI Garatya liye hea sys bi wis lo spurs Soke the wick, Rlstoleenn ee Te oe a a 1041 
LOCATION OF THE GONADS 
The gonads of the Arenicolidae are located on blood vessels 
which run diagonally across the surface of the nephridia. 
The typical somites of these worms are composed of five annuli, | 
one of which bears the setae. Three annuli are anterior andone 
posterior to this setigerous one. ‘There are six pairs of nephridia 
in Arenicola cristata, situated in the fifth to the tenth somites 
inclusive, a pair for each somite. Each nephridium consists of a 
funnel, body and bladder. The funnel has a sagittate dorsal 
lip set with ciliated plates and a lobed convex ventral lip; between 
the lips is the nephrostome. The body is club-shaped and con- 
nects, near its larger anterior end, with the funnel, at its posterior 
end with the bladder. The bladder is roughly spherical and opens 
to the exterior by a narrow tube through the nephridiopore. 
Each funnel is attached by the outside of the dorsal lip to the 
ventral surface of an oblique muscle, at some little distance from 
the attachment of the muscle to the body wall; so that the apex 
of the arrow-shaped funnel points downward and forward. The 
body of the nephridium passes up, back, and outward from its 
juncture with the funnel, to the bladder, which lies against the 
body wall close to the line of insertion of the oblique muscles to 
the sides. 
METHODS 
The ordinary method of pinning the animal out for dissection 
so pulls the nephridia that the shape, particularly of the delicate 
funnel, is distorted. The method followed has, therefore, been 
(1) to stupefy with 70 per cent alcohol, adding it rapidly, drop 
by drop, to just enough sea water, in a long dish, to cover the ani- 
mal. Stupefaction, with complete relaxation of the powerful 
muscles of the body wall ensues, in A. cristata, in from ten to thirty 
