566 H. p. KJERSCHOW AGERSBORG 



regions of the acini in Onchidiopsis are not demarcated 

 with any regularity, that in the middle portion male and female 

 acini can be seen in sections lying side by side. Also, that 

 the products of the two sexes either do not arise in the 

 same caecum or they do not arise in the same region of 

 a caecum. 



Bonne vie (1916) finds that Cuvierina colu nine 11a is 

 protandric ; the spermatozoa pass into the ' Zwittergang ' 

 and then the eggs develop ; there being only one ripening of 

 the germ-cells in the life of the individual. If this be also the 

 case among individuals of Aeolidia(Coryphella) lands- 

 bur gii, as reported by Pelseneer (1895 : 23), that the acini 

 of the hermaphrodite gland produce ova in their distal portion 

 and spermatozoa in their proximal portion, it is not so difficult 

 to understand how the product of the peripheral region of the 

 acinus with only one duct system may gain access to the duct, 

 the ripe spermatozoa simply passing out of the way, giving 

 its former position to the oncoming mass of the ripening ova. 

 Pelseneer reports that the same condition as noticed in 

 Aeolidia lands bur gii has been recognized as general 

 in all the Elysioidea (Cyerce, Hermea, Elysia, and 

 Limapontia). Mazzarelli (1891 o) found male and female 

 germ-products present at the same time in the acini of Aply- 

 s i i d a e , and in P 1 e u r o b r a n c h a e a separate male and 

 female acini. ' In the former there are only spermatozoa and 

 spermatids in varying stages of development, and spermatozoa 

 with sheaths (fascetti) seem joined together by cytophors. 

 In the latter (female acini) there occur only ova. The tiny ova 

 in diverse grades of development lie distributed all around the 

 internal aspect of the wall of the acinus as an epithelium. 

 Of the original germinative epithelium there remains slight 

 traces. The ova which are larger and nearly being expelled 

 are found more or less in the centre of the lumen. This fact, 

 that of the formation of spermatozoa and of ova in separate 

 acini in the male-female gland which is abnormal in the 

 Tectibranchs , is seen to be true or ordinary in effect in 

 many Nudibranchs.' 



