ZOOLOGY AND BOTANY, MIGEOSCOPYj ETC. 873 



verted (by invagination) into the gastrula, a certain number of meso- 

 dermic cells put in their appearance. The position of the blastopore 

 is with difficulty distinguishable, and its ultimate fate is unknown. 

 The anterior end is early distinguished by a small ectodermal 

 thickening, which is the rudiment of the future cerebral ganglion. 

 This thickening soon separates from the ectoderm and takes on the 

 form of a transversely widened plate, soon to be distinguished into 

 two halves. 



At the inferior pole a mass of cells begin to give rise to a pyri- 

 form organ, which is, physiologically, an excretory organ, and mor- 

 phologically interesting from its relations to the proboscis and its 

 resemblance to a similarly placed organ in the larvae of Annelids. 

 The mesoderm forms at first a simple layer, but soon gives rise to 

 a muscular and a splanchnopleuric layer, but at the anterior end 

 of the body no coelom is developed, and here the mesoderm forms 

 the connective tissue which surrounds the different organs of the 

 head. 



Before the cleavage of the mesoderm a saccular cavity is formed 

 around the proboscis, which grows very rapidly and extends to the 

 hinder end of the body. This is the sheath of the proboscis, and it 

 is absolutely independent of the coelom. Its first rudiment has the 

 form of a thick layer of cells surrounding the rudiment of the pro- 

 boscis ; it then divides into two layers, which are only single, for the 

 future, at the lower end. The three blood-trunks arise before the 

 formation of the body-cavity, and a rhythmical contraction is apparent 

 very early. 



In the intestine the digestive cells appear to multiply during the 

 whole of the life of the Borlasia, and to lead to a complete disappearance 

 of the lumen of this canal. The lateral nerves appear from comparative 

 data to be the homologues of the ventral chain of Annelids, but em- 

 bryological facts offer certain difficulties to this interpretation; the 

 rudiments of the lateral nerves are always distinctly separated from 

 the ectoderm, and seem to be direct prolongations of the cephalic plate ; 

 the author is inclined, therefore, to believe that the lateral nerves of 

 Nemertines are the homologues not of the ventral chain, but of the 

 peripharyngeal commissure of Annelids ; in connection with this, 

 we would quote the late Prof. Balfour : " A circumoral nerve-ring, if 

 longitudinally extended, might give rise to a pair of nerve-cords 

 united in front and behind, exactly such a nervous system, in fact, as 

 is present in many Nemertines."* 



New Human Cestode— ligula Mansoni.t— Dr. T- S. Cobbold 

 describes a Cestode, twelve of which were found in a Chinese, lying in 

 the subperitoneal fascia, about the iliac fossae, and behind the kidneys, 

 a single one being found lying free in the right pleural cavity. They 

 were from 12 in. to 14 in. long, l-8th in. broad and l-64th in. thick. 

 The Cestode comes nearer to Ligula simpUcissima, frequently found in 



* Comp. Embryol., ii. p. 312. 



t Joiun. Linn. Soc. (Zool.) xvii. (1883) pp. 78-83 (4 figs.). 



