460 
SUMMARY OF CURRENT RESEARCHES RELATING TO 
of the previous single chromosomata, or about a half of the double 
chromosomata. The author believes in the continuity of the cbromo- 
somata and in a cohesion of those previously distinct, a cohesion during 
which there is an interchange of material. He believes in a mutual 
fertilization — an amphimixis — of chromosomata, “ a hypothesis not 
unwarranted in the present state of our knowledge.” 
Development of the Lamprey.* — Dr. Ph. Owsjannikow publishes 
some of the results of his prolonged study of the lamprey’s development. 
The germinal vesicle in the very young ova with semi-fluid contents is 
often excentric. The Graafian follicles are invested by endothelial 
cells ; the blood-vessels enter at the pointed end of the follicle, within 
which lies the active pole of the ovum. The length of development 
varies with the temperature ; at 16° Reaumur the larvae hatched in nine 
or ten days. The first two planes of segmentation are longitudinal, the 
third is equatorial. The segmentation and gastrulation are described. 
The endoderm is formed by the separation of a row of cells from the 
yolk. The nerve-cord is at first solid, but subsequently exhibits a canal. 
Anteriorly the notochord arises as a double fold from the endoderm, 
and in other regions by a simple constriction. Unlike Shipley, the 
author does not find that the Wolffian ducts arise before the proto- 
vertebrae. As regards the origin of the sense-organs, previous observa- 
tions are confirmed. As to the heart, Shipley’s conclusions are in the 
main accepted. The endocardium arises in close association with 
the myocardium, and Goette erred in referring it to endoderm. In 
contradiction to Kupffer, Owsjannikow maintains that a neurenteric 
canal is distinctly demonstrable. Concerning the nervous system, it is 
noted that the hypophysis originates from ectoderm ; that all ganglia 
— both cranial and spinal — have an independent ectodermic origin ; 
that the spinal ganglia persist for some time with ectodermic connec- 
tions, though not yet united with the spinal cord, by the sides of which 
they lie. 
B. Histolog-y. 
Origin and Development of Muscular Tissue.t — Prof. G. H. T. 
Eimer is of opinion that there can be no doubt that the cross-striation 
of the highly developed musculature of Insects is only the expression of 
a temporary physiological condition. This cross-striation may dis- 
appear, reappear, and take on very various forms ; although, from an 
early stage, it exhibits a definite segmentation. At first, as in the 
adductor muscles of Lamcllibranchs, it is only transitory, and of the 
simplest character, without intermediate discs. In other cases it is 
constant. This incomplete cross-striation is seen in muscles that are 
comparatively inactive, and especially in lower animals, though also in 
Arthropods. The higher development of the cross-striation, when there 
are intermediate discs — the complete cross-striation — may be simple or 
compound. It is the latter, when the middle disc is divided into two or 
more. The alternation of a transverse and an intermediate disc is the 
ground-form of complete cross-striation. This ground-form is, in the 
* Melanges Biol. (Bull. Acad. Imp. St. Petersb.) xiii. (1891) pp. 55-67. 
f Zeitschr. f. Wiss. Zool , liii. Suppl. (1892) pp. 67-111 (13 figs.). 
