TUNICATA OF THE PRJBILOF ISLANDS. 535 



or not this would signify that the test of the embryo serves in any way as a medium of 

 nutrition I do not know. The mere fact of the presence in the test of i^arental sub- 

 stance that might be used for food by the embryo would not iirove that it actually is 

 so used. Both the fibers and the bodies which I have described and figured are, as a 

 matter of fact, either imbedded in or only slightly beneath the surface of the embry- 

 onic test, and their presence there may signify no more, so far as the nutrition of the 

 embryo is concerned, than do the great variety of foreign bodies that may be found 

 imbedded in the test of almost all tunicates. Nevertheless, the facts as presented 

 do undoubtedly raise this very interesting question, and there is certainly some ground 

 for suspecting that the test in these embryos does actually play a part in the nutritive 

 function. 



All the developmental stages that I have found earlier than the tadpole were 

 contained in a single post-abdomen. This had evidently been quite recently set free 

 from the zooid, since it still retained nearly its usual form and size. It was 4 mm. long 

 and quite narrow as compared with the almost perfectly spherical shape assumed at 

 a later time. 



It only remains to say a few words about the fertilization of the ova. I have 

 found fully developed sijermatozoa in several post-abdomens, but not in any of those 

 containing embryos. I have, however, seen so few post-abdomens with embryos in 

 the early stages of development that I would not venture to conclude that the same 

 individuals never do contain both ripe sperm and ova at the same time, and hence 

 that self-fertilization does not take place. In fact it appears exceedingly probable 

 that this is the method of fertilization. Certain it is that ripe sperm and well- 

 developed ovarian ova occur together in the same abdomen, and it is difficult to 

 conceive either that self-fertilization would be avoided in such cases, or how it could 

 be accomplished in any other way after tlie post-abdomens have become set free and 

 fully and deeply imbedded, as they do, in the hard test of the colony. 



In conclusion, I must express my regrets that I have not suflScient material to 

 make i^ossible a fuller account of the interesting processes here seen in outline only. 

 The facts are sufficient, however, to render this outline quite distinct, and we may 

 hope that opportunity will come before many years to fill in more of the details. 



Berkeley, February 17, 1898. 



EXPLANATION OF FIGURES. 



Fig. 1. Dendrodoa tuberculata, natural size. 



Fig. 2. The branchial and atrial orifices of D. tuberculata, with their adjacent parts, seen from the 



inside. 

 Fig. 3. The left half of the branchial sac of D. tuberculata, seen from the inside. 

 Fig. 4. Small portion of the branchial sac oi'D. tuberculata, from the inside. 

 Fig. 5. The ovary, in place on the mantle, of D. tuberculata. 

 Fig. 6. Genera] view of D. subpedunculata, natural size. 

 Fig. 7. A group of eleven individuals of I), subpedunculata attached to a fragment of seaweed. Two 



of these fused together. 

 Fig. 8. Specimen of D. tuberculata dissected to show the digestive tract and ovary in outline. The 



bands at x, and having considerable resemblance to the ovary, are folds in the mantle. (See 



note under description of species in the text relating to position of parts in this figure.) 

 Figs. 9 and 10. Styela greeleyi. 

 Fig. 11. Branchial sac of S. greeleyi. 

 Fig. 12. Digestive tract and sexual organs of same species. 



