66 BULLETIX: MUSEUM OF COMPAEATITE ZOOLOGY. 



observation of these relations, and a number of facts are now at band 

 which bear upon the subject. 



Ziegler ('95) has studied the cleavage of certain nematodes (Diplo- 

 gaster longicauda, Khabdites teres, and Ehabditis nigroveuosa) with 

 especial reference to the relations of cell form to the direction of cleav- 

 age, and finds that the conditions in these cases confirm throvghout the 

 late of Herhcig. In the normal cleavage the spindle always places 

 itself in the long axis of the cell, even though a rotation of the nucleus 

 and asters from their first position is often necessary to accomplish this 

 result. And in cases where the egg is deformed by some outer agent, 

 as pressure by the walls of the oviduct or the like, the normal position 

 of the spindle is changed to agree with the changed form of the cells, 

 the spindle lying in the long axis in every case. The agreement with 

 Hertwig's law is complete. 



On the other hand, zur Strassen ('95 and '96) has studied the cleav- 

 age of another nematode, Ascaris megalocephala, with the same ques- 

 tions in mind, and has come to opposite results. In the two-cell stage 

 one cell divides with the spindle in the long axis, the other with the 

 spindle in the short axis, and in later stages a similar independence of the 

 position of the spindle and relative dimensions of the cell is shown. Zur 

 Strassen ('95, p. 8G) concludes : " Ich halte vielmehr den Kern fiir be- 

 fahigt, vermoge ihm inhaerenter Eigeuschaften eine gewollte Theilungs- 

 richtunc heibeizufiihren, selbst wenn mechanische Hiudernisse von nicht 

 unbedeutender Hohe dem entgegenstehen." 



Other observations bearing upon this question are much scattered. 

 Cases are not uncommon in which authors have figured spindlesin the 

 shorter axes of the cells, but unless the observer's attention has been 

 especially directed to the question, such figures are of little value, since 

 a slight change in the position from which the cell is viewed produces a 

 foreshortening which gives very different apparent relative dimensions to 

 the axes. Heidenhain ('95, p. 553) gives a number of such cases, from 

 most of which the evidence is weakened by this consideration. How- 

 ever, the case mentioned by Heidenhain of the germinal disk of the 

 cephalopod egg as figured by Watase ('91) cannot be explained away 

 upon this ground. 



Some other instances may be mentioned. 



In the formation of the *• germ bands " in the Polychaet Amphitrite, 

 according to Mead ('94, p. 467), "the axes of the spindles in these 

 divisions lie in the shortest diameter of the cells, and apparently in the 

 direction of greatest pressure." 



