17 205 



since, of several species, we know rallier peculiar varieties, which almost in all 

 localities where the species occur, appear rather suddenly and then disap])ear 

 again. How much stress we are able to lay upon thai poinl is howcvei- questionable 

 as some of these varieties carry as well male eggs as female eggs. This is the case 

 f. i. with Polijnrlhra plalyptera var. eiiryptera. Already Roussklet (1896 p. 265 Tab. 

 XI. lig. 2) has shown this. 



With regard to the modes I have used to study the structure of Ihe males, 

 the following information may be given. As the males of almost all the species 

 are extremely small, it was very difficult to isolate them. Most of them have only 

 a size of about 100 /<; many only 40 — 50 //. Males which are more than V» mm. may be 

 regarded as veritable giants and occur mainly among the Asplanchnadœ, and some ge- 

 nera of Notommatidœ. The isolation was done by extremely fine pipettes, by means 

 of which they, after having been detected under a Seibert Microscope lensen Obj. 

 Oc. 0, were sucked up and brought under a Zeisz Microscope. The drop of water 

 was then made as small as possible, and a cover laid directly upon the drop, no 

 waxfeet were used. Commonly there was sufficient water under the cover for the 

 free swimming motion of the male; owing to slow evaporation of the water, the time 

 arrived when the male was found to modify its motions; asphyxia owing to dimi- 

 nution of the amount of oxygen or to the accumulation of carbonic acid caused 

 the animal to lie in the same spot, motionless, but with the wheel-organ wholh' 

 stretched out and with the cilia moving in the water. In this situation the animal 

 could live from thirty to sixty minutes and in this time it was studied and 

 drawn. Commonly there were in the vessels many or very many males of most 

 of the species; if so, male after male was used. The animals were lying with- 

 out any motion at all, and it was possible to draw them with Abbes camera. The 

 lenses which were used, were almost always homogen immersion Apochrom. 2 mm. 

 and Comp. Oc. 6, if necessary also the excellent Orthoscopical ocular, which with 

 hom. im. gave the power of 1500 times. A strong electric lamp was almost always 

 necessary. The greatest difficulty was to watch the male under low power, often 

 for hours, until that moment arrived when the animal had ceased to move. 



When studying the male under hom. immersion, it could further be shown 

 that, when the time arrived when the strength of the animal was almost exhausted 

 and the cover slowly pressed it more and more, the different organs appeared, one 

 after one, with increasing clearness; this was due to the stronger and stronger com- 

 pression of the hypodermal layer. 



All drawings are made bj^ means of Abbes camera ; as however the males did 

 not live for more than an hour, and often many males were used, many drawings 

 of the same males were worked out, whereupon all the drawings were combined 

 into one single one; commonly the outer contour of a male was given from one 

 specimen, and the anatomical details from another or very often from a whole series 

 of males. 



Narcotic fluids and staining fluids have only been used for the largest males, 



D. K. D. Vldensk. Selsk. Skr., naturv, og muthem. Afd., 8. Bække. IV. 3. 28 



