68 



BULLETIN : MUSEUM OF COMPARATIVE ZOOLOGY. 



The shape of the head varies greatly in different species, being short 

 oval, slender oval, rod-like, conical, needle-like, or even curved and 

 needle-like. Sometimes closely similar species exhibit considerable 

 difference in the shape of the spermatozoa. 



Reproduction. — In all except a few species of nemerteans the 

 sexes are separate and the sexual products when mature are dis- 

 charged through the genital ducts into the water in which the 

 worm lives. In some cases practically all the genital products in the 



Fig. 28.— Carcinon.emertes epiaUi. Transverse section of body showing the large 

 number of spermaries {t) and tlieir distribution through body parenchyma. 



body are discharged at the same time, while in other forms the 

 deposition of ova or spermatozoa may occur at intervals of a number 

 of days, so that several clusters of eggs or several emissions of 

 spermatozoa may result. 



Although in such cases there is no union of the sexes yet the 

 presence of a delicate sexual instinct among the nemerteans is indi- 

 cated by the observations of Mcintosh ('73) and confirmed by those 

 of C. B. Wilson (: 00), who found that in Cerebratulus lacteus the 

 discharge of ova by a female in one portion of an aquarium was 

 accompanied by the simultaneous emission of spermatozoa by another 

 worm living in another portion of the aquarium. 



In many species, especially of the Iloplonemertea, the eggs are 

 deposited in gelatinous masses of secretion beneath the stones or in 



