345 



consequently rendering unriecessaiy a union of the sexes, and 

 thus counterbalancing any loss occasioned by the conditions of 

 development. 



The eggs of Helminths are exceedingly minute, being scarcely 

 visible to the naked eye. They are so light as to readily float in 

 water, or to be transported by the slightest movement of the air. 

 They may likewise be disseminated in numerous ways, their hard 

 and horny shells and their minuteness serving to protect them 

 from injury. The eggs of tapeworms, as far as is known, and 

 those of most spindleworms are destined to be swallowed with the 

 food or drink of certain animals, in the intestine of which the 

 embryo hatches. The embryos of some spindleworms and prob- 

 ably those of all suckworras and hairworms can hatch, only in 

 water, where the eggs must arrive by chance, as in suckworms, 

 or be deposited by the mother, as in hairworms. It is unknown, 

 as yet, what becomes of the eggs of hookworms. But the em- 

 bryos of tapeworms, suckworms, and hookworms, and, as it 

 appears, also those of many spindleworms, reach, in the first ani- 

 mal into which they enter, only a limited degree of development, 

 and never the perfect stage ; that being achieved only in the 

 intestine of another entirely different carnivorous or insectivorous 

 animal, of which the first was the predestined food. In this, 

 likewise, we see the number of Helminths based upon chance, 

 those embryos which are necessarily lost in the first animal when 

 it has not been swallowed by another animal proper to per- 

 fect them, being taken into the calculation. 



Most Helminths perfecting their development in the intestine, 

 their eggs reach the outer world readily ; but it is difficult to say 

 how the eggs of certain species, which live in organs not commu- 

 nicating with the external world, like blood-vessels, can make 

 their way out. Still more difficult of explanation is the case of 

 the viviparous Helminths. In many species of spindleworms, for 

 instance, the common Oxyuris vermicularis of the human rectum, 

 the young is born without any shell to protect it in its wander- 

 ings, and is therefore extremely exposed to the danger of being 

 dried up or otherwise destroyed. 



Mr. Jerome G. Kidder was elected a Resident Mem- 

 ber. 



