14 
layer traversed by thick longitudinal muscle fibres. In this region 
are found the numerous nuclei belonging to both circular muscle 
layers, while the layers themselves are entirely free from nuclei. 
The thickness and firmness of the musculature must account 
for the rigidity of this flexible penis. In one specimen of hawaiiensis 
it is rolied up in a distal coil. 
Antrum masculinum has a tubular shape and runs almost dorso- 
ventrally with a slight backward direction, which shows that the 
characteristic of Leptoplanidae, i. e. the orientation of the copulatory 
organ in a rostro-caudal direction, has not entirely disappeared. 
The penis almost completely filis the tube-like antrum, and there 
exists no special penis-sheath (text-fig. 6 and 7). The antrum, how- 
ever, can be said to be divided into two parts through the histo- 
logical structure of the epithelium in the upper and the lower parts. 
The latter shows great likenes to the epidermis immediately around 
the male aperture. Glandular cells are thus absent here, and the 
differentiation consists primarily in the epithelium being less thick. 
On the other hånd, the intensive eosine stain in the outer zone 
of the epithelial cells belonging to the upper part of the antrum shows 
that here the epithelium has åcquired a special functional adaptation. 
This outer zone of the epithelium, i. e. the region outside the 
nuclei, is packed with tiny granulae that are stained deeply red 
with eosine. The drops are only about V 4 or Vs the size of the 
shell-secretion elements. The accumulation of the granulae in a 
peripheral zone only gives the cells quite a dissimilarity to the 
typical glandular cells, and the faet that these cells have well- 
developed cilia strengthens this impression. I have no reasons 
either to assume that this cell-content is emptied. It.does not seem 
probable to me that these bodies, which are eosinophile, should 
have the purpose of keeping the penis lubricated. In such a case 
it would not be likely that this occurrence of cells would be limited 
only to the upper part of the antrum. Such a funetion, however, 
could easily be attributed to a cyanophile secretion, produced, if 
such existed, by typical glandular cells (lacking cilia). On the 
contrary, I am inelined to assume that the existing granulae can 
play a part in the firmness of the cell. There might be a demand 
for this when the penis reaches its maximum expansion, when even 
the wall of the antrum is projected and becomes, so to speak, the 
