Minot.] 208 [April 2, 
As regards the echinoderms I refer to Selenka! and Gotte*, who de- 
scribe with unquestionable clearness the development of the meso- 
derm out of the amoeboid cells, of which it is at first solely com- 
posed. Upon worms but few investigations concerning the origin of 
the mesoderm have been made; in Phascolosoma Salenka® states that 
‘« Blutzellen” arise from the entoderm, and entering into the cavity 
between the two primitive layers, these represent the first cells of the 
mesoderm; there cannot be much doubt that these so-called 
‘“‘Blutzellen” are the primitive mesamoeboids. In other forms no 
mesamoeboids have been described — for example in the Nemertines 
Barrois* traces the mesoderm to epithelial discs, belonging to the 
original ectoderm, but his observations seem to me by no means sat- 
isfactory upon this point, and when he describes the delamination of 
the blastula in Amphiporus (i.c., p. 146 of the reprint) as resulting 
in the formation of the ectoderm and mesoderm, at a time when the 
entoderm does not yet exist, he assumes a method of formation of the 
germinal layers without parallel or analogy — for the portion which 
he designates as mesoderm corresponds in position and histological 
structure to what has been found to be the undoubted entoderm in 
other animals. The same difficulties of incompleteness renders it 
impossible to decide the problem in hand by reference to other in- 
vestigations —though Biitschli® mentions no amoeboid -cells in 
Cucullanus, but on the contrary figures the mesoderm in its earliest 
stage as an epithelial plate. 
In the case of several invertebrates there are said to be two large 
cells filled with yolk granules, and serving as the origin of the meso- 
derm. ‘These instances are Lumbricus®, Unio’, Pedicellina’, and 
1Selenka. Zur Entwickelung der Holothurien. Zeitschr. f. wiss. Zool., XXvVII, 
156. Taf. x1, figs. 19-21. 
2Gotte. Vergleichende Entwickelungsgeschichte der Comatula mediterranea. 
Arch. f. Mikr. Anat., XII, (1876), p. 587. Taf. xxv, figs. 1-5. 
3 Zeitschr. wiss. Zool., xxv, 442. r 
4J. Barrois. Mémoire sur l’embryologie des Nemertes. Am. Sci. Nat., Zool., 
S. vi, T. vi, (1877). 
5 Bitschli. Zur Entwickelungsgeschichte des Cucullanus elegans. Zeitschr. 
wiss. Zool., XX VI, (1875), p. 104. 
6 Kowalvseky. Embryologische Studien an Wiirmer und Arthropoden. Mém. 
Acad. St. Pétersb,, XVI, (1871). 
7 Rabl. Ueber die Entwickelungsgeschichte der Malermuschel. Jena. Zeitsbhr., 
xX, 347. 
