298 Tlie American Naturalist. [April, 



like a screw propeller, moves the essential head through the 

 water or along the ducts. 



Fertilization consists in a union of the spermatozoon with 

 the ovum. Many devices are developed to bring the two cells 

 near together, but they are then left to conjugate at will, as it 

 were. The road that it is necessary for the spermatozoon to 

 pass over to reach the ovum is frequently quite long, being in 

 the hen about 60 cm. and in large mammifers from 25-30 

 cm. But they are katabolic little creatures. It is wonderful 

 how such frail creatures can manage to overcome such obsta- 

 cles. Henle has seen spermatozoa carry along masses of crys- 

 tals 10 times larger than themselves. Pouchet has seen them 

 carry bunches of from eight to ten blood corpuscles. They 

 have been estimated to carry burdens four or five times 

 heavier than themselves without much difficulty or incon- 

 venience. 



Foil's Observations on the Union of Pronuclei? — Herman Foil 

 describes the phenomena of fecundation in the egg of the sea 

 urchin in about the following manner. The spermatozoon 

 five minutes after entering the egg is conical and from its tip 

 a small corpuscle, the spermocenter is detached (fig. 24). The 

 spermatic pronucleus swells and approaches the female pron- 

 ucleus the spermocentre in advance (fig. 25). The ovocenter 

 is located on the side of the female pronucleus opposite to the 

 side which gave rise to the polar globules. The spermocenter 

 becomes placed at the pole on the side opposite the ovocenter 

 (fig. 26). There are now two prolonged phases the " solar " 

 and the " aureolar ; " at the end of the first of these the ovocen- 

 ter and spermocenter becomes divided in the form of" halters, * 

 as the author expresses it, which are not placed in the same 

 plane. These " halters " come to lie parallel to each other in 

 the plane which will be that of the aureole (fig. 27.) In the 

 next phase the spermocenter and ovocenter become divided 

 (fig. 28) and the halves passing in opposite directions along a 

 fourth of a circumference of the combined nucleus arrive at a 

 point at right angles to their previous position. This Foil 

 calls the " Marche du quadrille. " 



