ENTEROPNEUSTA. 591 



The vascular system consists of a dorsal and a ventral vessel lying in 

 the mesenteries, and connected in the collar by an oblique vessel on each 

 side. The dorsal vessel enters the proboscis and ends in a sac, with 

 muscular walls lying immediately above the outgrowth from the digestive 

 canal. This sac is pulsatile, at least in the larva, and may be termed 

 ' heart.' There is a system of blood sinuses beneath the epidermis and in 

 the walls of the digestive tract. The blood contains no corpuscles. It is 

 said that the current runs forwards in the dorsal, backwards in the ventral 

 vessel. A peculiar structure lies above, in front of, and at the sides of the 

 heart in the proboscis. It forms the proboscis gland of Bateson, the 

 internal gill of Spengel. Its posterior part is saccular, while its anterior 

 and lateral parts consist of a network of blood-vessels covered with cells. 

 As these cells contain brownish granules, found also outside them in the 

 proboscis cavity, the organ is probably excretory (Bateson). 



The sexes are separate, and the sexual glands consist of simple or 

 branched sacs derived from the epidermis (?), opening by external pores, 

 and placed in lobes of the body-walls, which are arranged in a single 

 series to the outer side of the branchial pores, and extend behind the 

 branchial region to a variable distance. The larva of B. Kowalewskii is a 

 cylindrical organism with an anterior tuft and a posterior ring of long 

 cilia. The body is covered with short cilia, and the collar is early separated 

 off from the proboscis and trunk by two constrictions (Bateson). In other 

 species (? all) the larva is known as Tornaria. It has cilia arranged in a 

 prae-oral, and a longitudinal post-oral or oblique dorso-ventral band, and 

 in one or two, posterior rings. Two eye spots lie at the anterior extremity. 

 It resembles very closely the Bipinnaria larva of Asteroidea. 



The various species of Balanoglossus differ from one another in minor details. 

 The development of B. Kowalewskii has been accurately investigated by Bateson. 

 It may be noted that the proboscis gland originates, like the mesoblast, from the 

 wall of an archenteric outgrowth, and that there is neither stomo- nor procto-daeum. 



Bateson has proposed to class the Enteropneusta under the name Hemi- 

 Chordata with the Chordata. Of the points to which he draws attention, the gill- 

 slits formed as outgrowths from the digestive tract, together with their skeleton and 

 blood-supply, the origin of the mesoblast from enterocoelic pouches, the presence 

 of an anterior pouch, which is cut off from the archenteron and opens externally, 

 are undeniable resemblances to Amphioxus ; and it is possible that the backward 

 growth of the collar over the gill-slits, slight as it is, may be comparable to the epi- 

 pleural folds of that animal. But it must be borne in mind that the anterior 

 enterocoelic pouch is divided in Amphioxus into a left and right half, the former of 

 which is converted into a sensory organ, opening into the oral cavity. In Balano- 

 glossus Kiipferi, instead of one pore there are two, which lead into the interspaces 

 of the cells filling the proboscis cavity, and this may be an original feature. The 

 resemblance, therefore, between the structures is possibly only a general one. As 



