ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 
41 
occupies at most eight somites ; in the latter thero arc two, and in tho 
former three gizzards ; Trigaster has no caleiferous glands, its sper- 
mathecse are globular and without appendages ; there are no penial 
setm and no dorsal pores. Benhamia , on the other hand, has caleiferous 
glands, the spermathecae are ovoid, and have appendices to their narrowed 
ducts ; there are penial setae in special sacs, and some species, at any 
rate, have dorsal pores. Only one species of Trigaster is known, but 
there are already eight of Benhamia. 
Heliodrilus.* — Mr. F. E. Beddard has a preliminary notice of a new 
genus of Eudrilidae, which he calls Heliodrilus ; it has some resemblance 
to the lately described genus Hyperiodrilus, and, like it, it comes from 
Lagos, West Africa. There are six gizzards — one to a somite — at the 
junction of the oesophagus with the intestine. 
Development of Leeches.f — Dr. K. S. Bergh has a preliminary 
notice of the results of his investigations on the formation of layers in 
the germ-stripes of Leeches. In Clepsine the cell-rows are formed in 
the same way as in the earthworm ; of the four more superficially 
placed rows of cells, those which lie nearest the median line (I.) go to 
form the ventral chain, and may consequently be called, with Whitman, 
the neural row ; the three more lateral rows (II.-IV.) form the layer of 
circular muscles, and may, 'therefore, be called collectively the outer 
muscular plates ; they have no relation to the formation of the nepliridia. 
The deeper cell-row forms the so-called mesoderm, whence arise the 
blood-vessels, longitudinal muscles, loops of the nephridia, &c. 
Matters are more complicated in the Leeches with jaws, for, as is 
well known, the primitive epidermis is lost and replaced by a new and 
permanent one. This new epidermis consists of the descendants of the 
three lateral primitive cells ; in these, cell-divisions take place in various 
planes, and not only from before backwards, but also from right to left. 
In this way the germ-stripes increase in length and breadth, but do not 
give rise to any new layers. There are, however, other cell-divisions, 
which pass obliquely to the surface ; by these divisions some cells 
become separated from the superficial layer. These multiply, extend in 
length transversely to the longitudinal direction of the germ-stripe, and 
so form the circular musculature ; the superficial layer of the primitive 
cell-rows II.-IV. continue to grow and give rise to the permanent 
epidermis. The row (I.) nearest the median line here again forms the 
ventral chain ; it thickens and fuses with its fellow of the opposite side ; 
at first in a segmental manner in those regions which correspond to the 
later ganglionic parts. In the commissural parts they remain for some 
time distinct, and as the permanent epidermis is not yet formed, and 
there is no “ mesoderm,” there is at this stage a step-ladder-like appear- 
ance. So far as the author can see, some cells of the primitive nerve- 
cell-plexus take part in forming the ventral chain. 
The looped parts of the nephridia are formed from derivatives of the 
more deeply placed cell-row, but the epithelium of the contractile 
terminal bladders are invaginations of the permanent epidermis; the 
nephridia of the earthworm have nothing homologous to these terminal 
bladders. 
Zool. Anzeig., xiii. (1890) pp. 627-9. 
t T. c., pp. 658-60. 
