The Development of îschnochiton. 



571 



more over the mouth, until finally the dark end of the foot completely 

 conceals the mouth. I am unable to suggest any reasonable ex- 

 planation of the above mentioned peculiarity. 



2. Breeding Habits. 



The eggs of Ischnochiton are laid on those days of May and 

 June when the low tides come in the early morning. Unlike any 

 Chiton yet described, so far as I can learn, it does not lay its eggs 

 singly, but in "jelly masses". The oviducts between the ovary and 

 a point 8 or 10 mm from their exterior openings are modified to 

 form albumen glands (Fig. A), Just 

 before the breeding season these become 

 greatly distended and the eggs passing :^ 



out from the ovary are surrounded by , r Ç ' 



the secreted albumen and become 

 moulded by the lower end of the ovi- 

 duct into strings each with a diameter 

 of 3—4 mm and a length of about 

 77 cm. Along one side of the string 

 is a strip of albumen in which there 

 are no eggs. It is not in the state of 

 tension that exists in the remaining 

 albumen packed with ova, and con- 

 sequently the strings as they are laid 

 assume the form of spirals. 



It is difficult to find Ischnochiton 

 in the act of egg-laying, and the ob- 

 servations I have made along this line are few in number. They 

 have never bred in captivity, and the process in the normal state is 

 completed usually before daylight. Upon one occasion only I have 

 seen the method. It was in the early dawn and several specimens 

 were found out of water, having been left by the retreating tide, a 

 fact which probably accounts for their tardiness, since all the sub- 

 merged ones had laid. In each case the females were attached to 

 rocks, with the posterior half of the body protruded above the sand. 

 The free edges of the foot were expanded in such a way that they 

 sent wing-like processes across the gill furrows to the mantle. The 

 gills thus occupied tubular cavities, the ends of which were open 

 owing to a slight elevation of the posterior border of the mantle. 

 The egg strings had issued through the tubes thus formed, and several 



Fig. A. Ischnochiton magdalenensis 

 in the process of egg-laying. The 

 position of the ovary, albumen glands, 

 and oviducts is shown in stippled 

 outline. 



