476 A. M Verrill — Marine Planarlans of New England. 



merous, usually forming four groups, two of which are cerebral, and 

 two dorsal in the position of the tentacles of PlanoceridcB. Mar- 

 ginal ocelli sometimes present, often wanting or indistinct. The 

 copulatory organs are situated behind the mouth and more or less 

 distant from the posterior end of the body. The male organ is 

 directed backward. Male and female genital pores are usually con- 

 siderably separated, but sometimes have a common external opening. 

 In some genera a second female orifice is situated behind the ordin- 

 ary one. No marked metamorphosis. 



The species and genera of this family are not easy to distinguish 

 without a careful study, both of the living and prepared specimens. 

 The majority of the species, while living, closely resemble each 

 other in form, color, habits, etc., although the internal organs may 

 show great diversities in arrangement and structure. Unfortunately 

 it is generally difficult, if not impossible, to make out much of the 

 internal anatomy while the animals are alive, owing to the thickness, 

 density, and* imperfect translucency of the tissues ; the presence of 

 large quantities of ova ; the frequently deep colors, etc. On this 

 account the species, as collected, are frequently confounded, and the 

 rarer species, being mistaken for common ones, are often overlooked. 

 The only sure way, therefore, is to save all the specimens seen. 



Even the arrangement of the ocelli is apt to be deceptive, for 

 many very diverse species have the ocelli arranged in almost exactly 

 the same way. Moreover the number of ocelli and the forms of the 

 clusters in each species vary widely, according to the age of the in- 

 dividuals; and the form and relative positions of the clusters of 

 ocelli change greatly according to the states of contraction and ex- 

 pansion. In life, part of the ocelli are apt to be overlooked on ac- 

 count of their being more or less deeply imbedded in the integument, 

 and perhaps, also, partly concealed by pigment, as well as because 

 of their very small size in some species. The marginal ocelli, espe- 

 cially, are liable to be overlooked in several species, owing to their 

 minuteness. I have found it impossible to see the marginal ocelli 

 Avith the best of simple lenses, in some of our species, while they 

 were alive, but could see them easily when the same specimens were 

 properly preserved and mounted. 



The form is continually changing in life, and preserved specimens 

 are apt to contract in all sorts of shapes, unless care be taken to con- 

 fine them between glasses before killing. 



The colors of each species, in life, are usually variable through a 

 wide range of tints, and the special color-markings, when due to the 



