38 
SUMMAr.Y OF CURllENT RESEARCHES RELATING TO 
by an emi^ty space without proper walls, placed between the splanch- 
nopleure and the endoblast ; this may be considered as a blastocoel- 
space, which does not and never will communicate with the coelom. 
Later on, the splanchnopleure furnishes the vessel with a complete 
wall. When the two vessels are continuous along the whole of their 
course they give rise to anastomosing loops wLich unite the two. 
The seventh stage, in which the worm has thirty rings, is charac- 
terized by the appearance of the gonads and sperm-ducts. To begin 
with, the pair of nephridia 'in the eleventh ring is absorbed and disap- 
}3ears ; the rudiments of the testicle and ovary then appear in the 
eleventh and twelfth rings respectively; they are altogether derived 
from the peritoneal endothelium of the septum, which forms the anterior 
boundary to the ring in which they appear. The rudiments of the 
testicle grow rapidly, and divide into lobes, while the cells which form 
them become fused into a symplasm, in which a number of small nuclei 
are scattered. The rudiments of the ovaries remain undivided, and 
their cells, though closely packed, do not fuse. The two sperm-ducts 
appear in the twelfth ring in the place of the segmental organs, which 
are not there developed ; their origin and mode of development 
resemble in all points those of true nephridia ; so that the homology of 
the two sets of organs cannot be doubted. They are put into relation 
with the ectoblast of the wall of the twelfth ring to form the penis. 
In the adult stage the body of the worm measures 12 to 15 mm. in 
length, and has about fifty rings ; the clitellar region is a little wider 
than the rest of the body, owing to the thickening of the ectoderm, in 
which there are numerous mucous cells, and to the distension of the 
walls by the contained gonads. The author describes the phenomena 
of spermatogenesis and oogenesis. When the adult has discharged its 
gonads the tissues of the organs undergo degeneration, and the indi- 
vidual dies. The aet of reproduction appears, therefore, to be the term 
of life in this species. 
The absence of initial mesoblasts does not appear to be peculiar to 
the embryos of Eyichytrseoides ; it seems, on the contrary, to be the rule 
in all condensed develoj)mental histories of Annelids. Similar facts 
have been noted in other groups of animals, for, e. g. the enterocoele of 
Amphioxiis apj^ears to be wanting in most other Vertebrates, where the 
mesoblast is sej^arated by a simple cleavage of a primordial layer, which 
corresponds to the meso-endoblast of Annelids. When a mesoblast is 
formed in Enchytrseoides it is homologous with the mesoblastic bands of 
the larval trochosphere. The differences between the embryo now 
described and the trochosphere are due to the condensation of develop- 
ment in the former. The difference between the descriptions now 
given and those of the development of other Oligochaeta are consider- 
able, but are probably largely due to the want of technical appliances 
which obtained when these latter were drawn up. 
With regard to the systematic position of Annelids, M. Eoule agrees 
with Hatschek in allying them to the Mollusca ; it is very probable 
that both Annelids and Hatyhelminths were derived from a group of 
Coelomata which had a very simple structure, similar to that of the 
trochosphere- larvj. The whole group may be called the Trochozoaria, 
and divided into those that are polymeric or segmented and those that 
