ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 
481 
each side of the brain which corresponds to the neck-organ of other 
Annelids. The species in which the head-lobe has richly innervated 
anterior corners have otocrypts with foreign bodies (A. marina) or simple 
pocket-like grooves (A. Claparedii) ; the other two species are without 
the sensory protrusions and have closed otocysts with intrinsic otoliths. 
In A. Grubii the brain has a commissural structure and the neck-organs 
are widely open ; a concentration of the nervous mass and a contraction 
of the neck-organs are associated with the presence of otocrypts. 
The auditory organs do not arise from neck-organs. The latter 
are innervated from the brain, belong to the head-lobe, are con- 
stituents of the prosoma, and are perhaps comparable with paired sense- 
organs on the apical plate of the Trochophore The auditory sacs are 
innervated from the oesophageal ring. Nor can the sacs be compared 
with the seta- sacs of parapodia, for, apart from other reasons, both dorsal 
and ventral branches of the parapodia occur in Aricia acustica along 
with otocysts. Dr. Ehlers is rather inclined to regard the otocysts 
as organs substituted for cirri, and to believe that they may have been 
originally distributed in segmental order on the parapodial surface of the 
body. He concludes his memoir with a general comparison of lateral 
sensory organs. 
Encystment of Acolosoma and Earthworms.* — Prof. F. Vejdovsky 
brings forward evidence to show that the species of Acolosoma can form 
a true cyst. He compares with this the formation of special cavities by 
certain Lumbricidae, and he ascribes both sets of phenomena to the rest 
required after a period of asexual reproductive activity ; in other words, 
he compares them directly to the phenomena of encystment seen among 
Protozoa. 
Intestinal Cilia of Lumbricus.t — Miss M. Greenwood, who has been 
investigating the presence of retractile cilia in the intestine of the 
earthworm, finds that the digestion of food in this worm is effected 
mainly by a secretion which is found in the granules of unicellular 
glands. These gland-cells stand singly, and may be placed throughout 
the entire length of the typhlosole, and over a corresponding region of the 
walls of the intestine. The absorption of digested food appears to be 
carried out by the cells which surround the glands ; these are elongated, 
branch internally, and have no firm lateral connections. The edges 
which are turned towards the lumen of the intestine are expanded, and 
appear to meet over the depressed gland-cells. There is a hyaline basal 
band which is pierced by, or apparently gives rise to cilia ; during the 
digestion of fat any epithelial cell by which it is absorbed shows a 
striated external border which replaces the active cilia. These inges- 
tive cells are localized in a zone which recalls the mode of distribution 
of the unicellular glands, and they are more striking on the typhlosole 
than on the intestine proper. Cilia are absent at times from a much 
larger area of the typhlosole than that over which the ingestion of fat 
extends ; and it is, therefore, possible that there is a connection between 
the absorption of matters in solution and structural change in the epithe- 
lial cells. It appears possible that there is a certain excretion of solid 
* Zool. Anzeig., xv. (1892) pp. 171-5. 
f Journal of Physiology, xiii. (1892) pp. 239-59 (1 pi.). 
2 L 
1892. 
