14 COMMISSION OF CONSERVATION 



In measuring with such small units the larger the measurement the more correct 

 it is, for the difficulty of reading one or two units where even the thickness of the micro- 

 meter lines has to be considered, is liable to cause as great an error for one or two units 

 as in other cases would be spread over a great many. Spherical eggs measured with 

 Oc. V, obj. 4, give nearly 1\ (7ix6-9 = 51-75 n); with Oc. V, obj. 7, they vary about 

 35 (35 x 1-45 = 50-75 fi), while the head of a sperm-cell with Oc. V, obj. ^ is ap- 

 proximately 2 (2 x -875 = 1-75 p). 



Each spermatozoon (Plate V, fig. 4) possesses two distinct parts, a 

 head and a tail. The head is almost oval in form, somewhat pointed 

 anterior^, but inclined to be squarish posteriorly, where there are four 

 minute spherules, between which is inserted the tail. The head measures 

 approximately .00175 mm. in breadth, while the tail is fully twenty times 

 this length, becoming so fine towards the end as to be hardly perceptible. 

 A sperm-cell is much more highly specialized than an egg-cell, i.e., it dif- 

 fers more markedly from a typical young, living cell of the body, and this 

 is in adaptation to the special work it has to perform. It resembles in 

 shape and behaviour many fully organized, active animals. Its ability 

 to swim by violent flapping of its tail, its small size, and the vast numbers 

 produced, increase the chances of its coming in contact with and pene- 

 trating into an egg. Most of the head consists of nucleus, about which 

 the protoplasm is reduced to a minimum, and its brief life as an inde- 

 pendent organism does away with the necessity of its being encumbered 

 with food granules. Notwithstanding the fact that we are accustomed 

 to think of the egg only as passing by development into the larva, yet it 

 would seem that the sperm is just as important, and it is due to its relative 

 inconspicuousness and early disappearance that we forget it. Unfertilized 

 eggs soon die and disintegrate; it is only healthy eggs, normally fertilized, 

 that develop. The sperm infuses new life and vigour, and, besides, it is 

 the only means of carrying over hereditary characters of the male parent 

 to the offspring. 



Fertilization (Fecundation). — The male reproductive organ (testis) 

 occupies a like space in the body of the male oyster as does the female re- 

 productive organ (ovary) in the body of the female, and we would judge 

 that the male discharges an equal mass of reproductive matter. Ex- 

 amination of large numbers of full-grown oysters shows that the sexes 

 are approximately equal in numbers; as a consequence there would be 

 several thousand sperms for each egg spawned. This difference is further 

 increased by the circumstance that males become sexually efficient at an 

 earlier age than females. In the water about every oyster bed, in the 

 breeding season, the number of spermatozoa must be inconceivably great 

 — doubtless a provision of nature to insure that each egg shall have a fair 

 chance of becoming fertilized. It would look at first sight as if there were 

 little risk in this respect. But we must stop to consider that many males 

 may expel their spermatozoa when and where there are no eggs to be 

 fertilized, that the active life of a spermatozoon is limited to a brief period. 



