REVIEW OF SPENGEL’S MONOGRAPH ON BALANOGLOSSUS. 389 
The development has been worked out by Bateson as men- 
tioned above, the main points observed being the following :— 
The egg undergoes total and regular segmentation, and forms 
a one-layered blastophere. Regular embolic invagination fol- 
lows, giving rise to a gastrula, and the blastopore is situated 
posteriorly and slightly dorsally. It closes in the position 
about where the future anusis formed. The archenteron gives 
rise to an anterior and to two lateral pairs of pouches, as 
shown in fig. 6; the former becomes proboscis ceelom, the 
latter the collar and trunk ccelomic cavities. The noto- 
chord arises partly as an anterior diverticulum of the gut; its 
posterior part, however, is constricted off as a dorsal groove of 
the buccal cavity. The central nervous system is separated 
from the ectoderm by delamination, but is added to anteriorly 
and posteriorly by fore and aft invaginations from the anterior 
and posterior surfaces of the collar. The species on which 
Bateson worked develops up to a comparatively advanced stage 
within the egg-membrane, and hence its external larval cha- 
racteristics have been very much modified. The ordinary 
mode of development seems to be through a most interesting 
pelagic larva, Tornaria, the early history of which is unknown. 
This larva shows a very close resemblance to the Bipinnaria 
larva in the disposition of its cilia and in the possession of a 
preoral coelomic vesicle opening by a pore on the left side, 
whereas in the position of a well-marked apical plate, con- 
nected by a double muscular band with the sides of the ceso- 
phagus, it recalls certain features of the trochosphere. 
Morgan has made the interesting observation that the central 
nervous system in this larva is formed by the invagination of 
a strip of ectoderm exactly as in Amphioxus. 
The monograph of Professor Spengel commences with a 
detailed description of one of the Neapolitan species, which is 
chosen as a type. The other species are then described in the 
order of their affinity to this type. Next follows a chapter on 
the ontogeny. Then the special morphology of each organ is 
discussed in detail. To this succeeds a chapter on the general 
morphology of the animal, and finally there is a discussion of 
