242 CEPHALOPODA. 



The ciliated rings give to these larvae a resemblance to Chcetopod larvae ; 

 but there can be no doubt that this resemblance is a purely superficial one- 

 The anterior ring atrophies early (fig. 109 B), and the second one soon 

 follows suit. It is probable that the hindermost one does not persist 

 through life, although it has been observed in forms with fully developed 

 sexual organs. Most of these larvae have not been traced to their adult 

 forms. They have been referred to Pneumodermon, Clio, etc. 



The most characteristic organ of the Pteropods is the foot, which is 

 prolonged into two enormous lateral wings, the epipodia. These develope 

 at different periods in different larvae, but are always distinct lateral out- 

 growths of the foot. 



In the Hyaleidic the foot is early conspicuous, and soon sends out two 

 lateral prolongations (fig. 108 pn.} which develop with enormous rapidity 

 as compared with the medium portion, and give rise to the epipodia. The 

 whole of the foot becomes ciliated. 



In the Cymbulidae, though not in other forms, an operculum is developed 

 on the hinder surface of the foot (fig. 103 C). The epipodia are late in 

 appearing. 



In the Gymnosomata the foot is developed very early, but remains small. 

 The epipodia do not appear till very late in larval life (fig. 109 B). 



In Pneumodermon and some other Gymnosomata there appear on the 

 hinder part of the head peculiar tentacles with suckers like those of the 

 Cephalopoda (fig. 109 B). It is not certain that these tentacles are geneti- 

 cally related to the arms of the Cephalopoda. 



Cephalopoda. The eggs of the Cephalopoda are usually 

 laid in special capsules formed in the oviduct, which differ 

 considerably in the different members of the group. 



In the case of Argonauta each egg is enveloped in an elongated capsule 

 provided with a stalk. By means of the stalk the eggs are attached together 

 in bunches, and these again are connected together and form transparent 

 masses, which are placed in the back of the shell. In octopus the eggs are 

 small and transparent : each of them is enclosed in a stalked capsule. In 

 Loligo the eggs are enveloped in elongated sack-like gelatinous cords, 

 each containing about thirty or forty eggs. The cords are attached in 

 bunches to submarine objects. In Sepia each egg is independently en- 

 veloped in a spindle-shaped black capsule, which is attached to a stone 

 or other object. 



In a decapod form with pelagic larvae, described by Grenacher (No. 280), 

 the eggs were enclosed in a somewhat cylindrical gelatinous mass. In each 

 mass there were an immense number of eggs arranged in spirals. Each 

 ovum was enclosed in a structureless membrane, within which it floated in a 

 colourless albumen. 



The ovum itself within the capsule is a nearly homogeneous 

 granular mass, without a distinct envelope. Development com- 



