ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 
557 
Molluscoida. 
o. Tunicata. 
Vertebration of Tail of Appendiculariae.* — Mr. G. Lefevrc lias 
convinced himself that the interruption in the continuity of the muscle- 
fibres of the tail is artificial, and does not represent a true metamerism. 
With high magnification the ragged ends of the broken films may be 
seen, and in some cases the splits are not continuous, but are represented 
by zigzag rows of isolated clefts. Some specimens of OiJcopleura 
collected in the Gulf Stream did not exhibit the slightest trace of breaks 
of any kind in the muscle-fibres ; gentle stretching of the tails between 
forceps resulted, in some cases, in the production of eight transverse 
splits. There seems, therefore, to be little, if any, room for doubt that 
the vertebration of the tail of Appendicularians is an artefact, though 
the tendency of the muscle-fibres to break at definite intervals may be 
regarded as the first step towards vertebration; this is, of course, in 
opposition to Lankester’s view that it is a remnant of a more marked 
vertebration in an ancestor of the present Appendiculariae. 
Variations in the Dorsal Tubercle of Ascidia virginea.f — Miss 
A. E. Warham has, at the suggestion of Prof. Herdman, extended his 
observations on the variations of this organ. She is able to recognize 
two simple forms, of both of which there are some eight variants. 
Arthropoda. 
Walking of some Arthropoda.]; — Mr. H. H. Dixon has a preliminary 
note on the locomotion of various Insects, Spiders, and Scorpions. In 
his observations he used a quarter-plate camera with instantaneous 
shutter. In all the adults examined, except the Thysanura, the almost 
simultaneous motion of the “ diagonals ” is the rule, though instantaneous 
photography shows that it is not absolutely synchronous. 
a. Insecta. 
Formation of Germinal Layers in Insects. § — Dr. E. Heymons has 
investigated the history of the germinal layers in Phyllodromia ( Blatta ) 
germanica, Gryllotaljpa vulgaris , Gryllus domesticus , G. camjpestris, and 
Forjicula auricularia. In all but the second of these the yolk-cells 
were found to disappear during the course of development, without 
taking any part in the formation of the embryo ; the epithelium of the 
mid-gut, which only appears relatively late, does not arise from the 
lower cell-layers, but from the blind cords of the ectodermal stomodseum 
and proctodseum. From these two points cell-layers grow out to the 
middle of the body. The layer which corresponds to the endomesoderm of 
other authors appears to give rise to the fat body, the muscular system, 
blood-cells, &c., tissues which are ordinarily regarded as of mesodermal 
origin, and the author, therefore, calls it the mesoderm. The formation 
of the mesoderm has nothing to do with the invagination-process in a 
gastrula. It is a remarkable fact that the primitive groove may in 
* Johns Hopkins Univ. Circ., xiii. (1894) pp. 57 and 8 (3 figs.), 
t Trans. Liverpool Biol. Soc., vii. (1894) pp. 98 and 9. 
t Sci. Proc. Koy. Dublin Soc., vii. (1892) pp. 574-8. 
§ SB. Akad. Wiss. Berlin, 1894, pp. 23-7. 
1894 2 Q 
