J. FULLAGAR ON TUBICOLARIA NAJAS. 1>S3 



with it the particles of food on which the animal feeds ; the food 

 thus introduced into the mouth (Fig. 1 a), which is also lined with 

 long cilia, is thereby conveyed down to the grinding apparatus termed 

 the gizzard or jaws (Fig. 1 b), where it undergoes mastication, and 

 then passes into the stomach, where it is subjected to the process of 

 digestion (Fig. 1 c), and then proceeds to what is termed the lower 

 stomach (Fig. 1 d), where it is retained for some time in order to 

 perfect the process of digestion, and to extract that which is essen- 

 tial for the nutriment of the creature. The effete matter left is 

 thrown out by a curious motion of the intestine (Fig. 1 e), up which 

 it travels, and is discharged at f. The intestine, with the lower 

 stomach when empty, is seen to be thickly lined with vibratile cilia. 

 The ovum of T. Najas is formed in the upj^er portion of the body 

 (Fig. 2 g), gradually growing there until it has attained the full size ; 

 it then occupies about two-thirds of the body, and is of a dark-brown 

 colour. It progresses thus far within the body. The ovum being 

 now ready for expulsion, is slowly forced down to the lower part of 

 the body, the stomachs being drawn upwards, and on one side, in 

 order to make y ay for it. Yielding to the pressure produced by the 

 successive contractions of the body, the ovum passes down to, and 

 out through the oviduct (Fig. 2 h), and is lodged within the gela- 

 tinous substance with which the animal is surrounded (Fig. li). 

 When once the egg has begun to move downwards from its original 

 position, it occupies not more than two minutes before it is fully 

 expelled from the body. It then presents the form shown at Fig. 3 k, 

 is of a brownish colour, and reticulated, as though covered with a 

 network consisting of oval-shaped meshes. It gradually becomes 

 less opaque, and in about four days after extrusion the first trace of 

 life becomes visible, presenting itself in a few freely-moving cilia at 

 two points, one corresponding to the future head (Fig. 4/), the other 

 near the centre of the ovum. Shortly after, at the latter place, the 

 central parts of the dental apparatus or gizzard are seen in motion 

 at intervals (Fig. 4 m). The cilia at the head continue to increase 

 in activity, and the whole contents of the egg are seen to twist to 

 and fro, as the time of development draws near, but no definite form 

 of the future animal can be detected. Two dark spots now make 

 their appearance (Fig. 4 n), but what they are I have not been able 

 to make out. In two instances I had watched the progress of the 

 eggs almost up to the time at which the development should take 

 place, when 1 was obliged to leave them, and on both occasions, 



