No. 2.] ANURIDA MARITIMA. 275 
is in coarse threads (Fig. 62) or irregular masses (Figs. 59, 60). 
In the size and external characters of the animal the changes 
in the interval are marked, but practically no development has 
taken place in the reproductive cells. The external part of the 
reproductive organ, the outlet, was found to originate in the 
late embryonic stages by a median unpaired invagination from 
the hinder end of the fifth abdominal segment. As shown in 
the adult, the ectodermic part of these ducts is extremely short, 
being only the small unpaired part extending from the exterior 
through to the body space, where it joins the mesodermic part 
of the organ. This is found completely invaginated in late 
embryos, and showing in the female the accessory diverticula, 
the receptaculum seminalis, as a branch of the main duct. 
When it was found that the yolk was not contained in the 
mid-gut of the embryo, the question naturally arose as to its 
final disposal. It has been seen from the above facts that a 
large part of it is included within the reproductive organs, and 
serves to hasten very much the maturing of the generative 
elements. A very large quantity is also found in the blood 
corpuscles of the newly hatched animal. Fig. 63 shows some 
of these taken from the same animal as Fig. 59. Gradually 
during their circulation through the body they must give up 
their rich supply of food. No complete observations were made 
on the origin of these cells, but it is probable that they arise 
from the mesoderm. Already in Fig. 53 small isolated meso- 
dermic cells can be seen, and many are found later in different 
parts of the body. Even when loaded with yolk there is no 
possibility of confusing them with yolk-laden entoderm cells, 
they are so very much smaller in size (cf. Fig. 63 and Pl. XXII, 
Fig. 41; 63 is magnified more than 41). Yolk was found in the 
places already enumerated and also free in the body cavity, lying 
chiefly under the alimentary canal. Thickly scattered through 
the meshes of the connective tissue are many yolk spheres, 
which are eventually transformed into fat globules. When first 
hatched, the body cavity, as it is called, or, more correctly 
speaking, the haemocoele, is much obscured by a large amount 
of connective tissue that originates from the mesoderm. The 
alimentary canal, reproductive organs, and nervous system all 
