266 REPORT— 1851. 



are grouped into a lobulated mass at the median line. The utero-ovaria 

 occur as segmentally repeated sacculi, communicating on the ventral surface 

 of the body by perceptible orifices. In Terebella nebulosa the whole of the 

 sexual system may be readily demonstrated ; it lies underneath the alimentary 

 canal. To expose it to view this latter must therefore be removed. Along 

 the median line is accumulated under the form of white lobulated masses 

 the testicular glands. The secretion furnished by these masses is conveyed by 

 means of a common duct to a receptacle, a sacculus, situated at its anterior 

 extremity. This organ communicates externally by an orifice or two, through 

 which the spermatic fluid is emitted. During the contact of two individuals, 

 this fluid passes outside along the abdominal surface of the body, and thence 

 finds its way into the ovario-uterine organs, which exist to the number of 

 ten on either side of the abdominal median line, and which communicate by 

 corresponding orifices externally. 



The minute anatomy of these utero-ovarian organs in Terebella nebulosa, 

 is well calculated to elucidate the mechanism of reproduction in several other 

 species of Annelida. 



Each lateral utriculus is divided longitudinally into two distinct com- 

 partments, of which one is thicker (in the parietes) at the attached end, and 

 more vascular and redder in colour than the other, which is a mere mem- 

 branous receptacle. A small glandular mass exists at the attached end 

 of each of these organs, which during the reproductive season undergo a 

 remarkable increase of size ; they are true ova-producing bodies. From this 

 stromatous structure the ova escape into one of the compartments of the 

 utricle, where they fall under the influence of the spermatic fluid contained 

 (received from without) in the other. They sojourn for some time in this 

 receptacle, and finally escape as ova. The TerebellcB are therefore oviparous. 



The sexual system of Arenicola is organized on a plan which intimately 

 resembles that just described in T. nebulosa ; there are, however, in this 

 worm no median testicular masses. The male and female elements are at- 

 tached to the lateral sacculi, which in this worm, like T. nebulosa, are 

 arranged in lateral series, and divisible into two portions by a median parti- 

 tion. During the reproductive season these organs become highly vascular 

 and prominent. The Nereids are constructed, as regards their reproductive 

 sj-stem, very much on the type of that oi Lumbricus. Each segment is fur- 

 nished with its utero-ovarium. The Phyllodoce are organized on the same 

 principle*. 



Senses, Instinctive Actions, and Nervous System. 



The nervous system of the Annelida is constructed in conformity with the 

 articulated type. It is characterized essentially by the presence of a ganglion 

 on the dorsal aspect of the oesophagus, and hence called the cephalic or supra- 

 cesophageal; and another on the ventral surface of the oesophagus, known as 

 the infra-oesophageal. These two ganglia are united by means of intermediate 

 threads which descend on either side of the oesophagus, such as to embrace 



* Development of the Annelida. — I have not yet attempted the study of tlie embryology of 

 the Annelida j Milne-Edwards is the only observer who has contributed to this branch of 

 comparative physiology. It is not hkely to prove difficult of elucidation. From casual ob- 

 servations which I have instituted into this department of the subject of the Report, I do 

 not think that it will prove veiy difficult of elucidation. 1 by no means agree with Loven in 

 the accounts which he has given with reference to the metamorphoses of the Annelida. I 

 have never yet seen an instance in which the embryo of an Annelid has departed from the 

 true vermiform conformation. Appendages are successively developed during the progress of 

 gro^N'th, as figured in the illustrations of Milne-Edwards, in the instance of T. nebulosa. 

 Patience, truthfulness and exactitude are yet wanting to complete the department of the 

 history of the British AnneUda. 



