March 12, 1897.] 



SCIENCE. 



435 



Numerous amoeboid cells are always pres- 

 ent iu the uterus among the embryos. 

 These are probably concerned in the nutri- 

 tion of the embryos, since they may be seen 

 passing through the uterine wall, and the 

 uterus is surrounded by a great quantity of 

 cells filled with yellow granules, probably 

 of food material. 



Perhaps the most important develop- 

 mental point thus far made out is that the 

 peribranchial sacs arise as two tvell defined 

 ectodermal invaginations on the dorsal side of the 

 embryo. 



The results, then, support the conclusions 

 of Kowalevsky, Seeliger, Willey, Hjort and 

 Caullery on this head, and oppose those of 

 Delia Valle, van Beneden et Julin, Pizon 

 and Garstang, who hold, in one wa.y and 

 another, that these structures arise from 

 the endoderm. 



Notes on Chelyosoma productum, Stimpson. F. 



W. Bancroft. 



An examination of about 20 individuals 

 in the collections of the University of Cali- 

 fornia shows that this western ascidian is 

 quite distinct from its Atlantic and Arctic 

 representative, C. macleayanum. Stimp- 

 son describes the species as having the disk, 

 which is characteristic of the genus, divided 

 into fourteen plates ; but in the individuals 

 examined the number was found to vary 

 from thirteen to twenty. This variability 

 is associated with a muscular system that is 

 quite different from what is found in the 

 other member of the genus. In C. produc- 

 tum the systems of short muscles joining 

 adjacent plates are wanting, except around 

 tlie orifices, and are replaced by a series of 

 fibres extending from near the center of the 

 disk to its periphery and some distance 

 down the sides of the animal. The method 

 of attachment of these muscles is different 

 from that described for any other ascidian. 

 Both ends of every bundle of muscle fibres 

 are firmly attached to little projections of 



the inner surface of the test. On these the 

 ectoderm is thrown into deep folds and 

 pockets which greatly increase the surface 

 of contact with the test, so that the mus- 

 cles which are joined to the inner ends of 

 the ectoderm cells cannot tear them away. 

 The matrix of the test, like that of some 

 other tunicates, consists of an inner layer 

 of cellulose and an outer one, very dis- 

 tinctly separated from it, which is not cellu- 

 lose, and which corresponds to the ' yellow 

 layer ' of the early authors. In our species 

 it is easily seen that this outer layer is 

 formed from the cellulose matrix by the 

 activity of the mesodermic bladder cells 

 which the latter contains. The first traces 

 of the ' yellow substance ' are seen about 

 isolated bladder cells near the outer layer, 

 and all transitions can be traced from this 

 stage until the cell and the yellow sub- 

 stance it has produced are incorporated 

 into the outer layer. The other organs of 

 Chelyosoma are of a less exceptional char- 

 acter and clearly show that it is more closely 

 related to Corella than to any other genus. 



On the Plan of Development of a Myxinoid^ 



Bashfoed Dean. 



The marked dissimilarity in the develop- 

 ment of Bdellostoma and Petromyzon was 

 noted. In the former a large supply of j'olk 

 produces a merocytic condition at a very 

 early stage ; The head region of the embryo, 

 appearing first, very much as in Elasmo- 

 branchs, takes its position near the animal 

 pole ; the body region is then laid down, 

 apparently by concrescence, in an almost 

 straight line extending in the direction of 

 the yolk pole almost the entire length of 

 the egg. The subsequent growth of the 

 embryo constricts both head and tail from 

 the yolk sac, and in very late stages an em- 

 bryo of nearly two inches lies coiled within 

 the egg A preliminary study confirms 

 Professor Price' s observations as to the great 

 number of gill slits. 



