IxXXVi INTRODUCTION. 



We may probably also rank amongst the organs of 

 sense, though of a very humble and rudimentary kind, 

 the coloured specks, frequently inclosing a refractive 

 corpuscle, which occur on many of the Polyzoan larvse. 

 They are sometimes numerous (as in Bugula flabellata, 

 Plate LXXXIII. fig. 6)*, and may perhaps be regarded as 

 primitive eyes. 



Reproduction and Embryology. 



Two kinds of reproduction have a place in the life- 

 history of the Polyzoa, a sexual and an asexual — (i) re- 

 production by means of ova and spermatozoa, and (ii) by 

 gemmation f- 



In a large proportion of cases the species seem to be 

 monoecious, both male and female organs being present 

 in each cell. But the rule is not without its exceptions. 

 Alcyonidium gelatinosum, according to Kolliker, is uni- 

 sexual; and I believe the same to be the case with A. 

 tnytili. In this species the ova are produced in gonoecia 

 (that is, in cells destitute of a polypide and devoted to 

 reproductive functions), whilst in some of the ordinary 

 zocecia the spermatozoa occur in enormous quantities : I 

 have seen them darkened by the dense mass of wriggling 

 filaments which filled the perivisceral cavity. Such cells 

 were provided with the ciliated intertentacular organ (to 

 be described hereafter) ; and through this the spermatozoa 

 Avere finally discharged into the surrounding water. In 

 this case it would seem probable that the sexes are distinct; 



* Nitsche, " Ueb. die Entwicklungsgeschiehte einiger chilostomeii Bryo- 

 zoen," Zeitsch. f. wissensch. Zool. xx. Heft 1, p. 7 (sep.). 



t Sexual elements have not yet been observed in the Cijclo&tomata. 



