Arthur Willey

“ An important feature is the occurrence in some species (Ptychoderidae) of paired longitudinal pleural or lateral folds of the body which are mobile, and can be approximated at their free edges so as to close in the dorsal surface, embracing both the median dorsal nerve-tract and the branchial grooves with the gill-pores, so as to form a temporary peri-branchial and medullary tube, open behind where the folds cease. ”

“ It is within the bounds of possibility that Tornaria actually does indicate a remote affinity on the part of the Enteropneusta to the Echinoderms, not only on account of its external form, but also by reason of the possession of a dorsal water-pore communicating with the anterior body-cavity. In the direct development Bateson showed that the three divisions of the coelom arise as pouches constricted off from the archenteron or primitive gut, thus resembling the development of the mesoblastic somites of Amphioxus. ”

“ Development.—The development of Balanoglossus takes place according to two different schemes, known as direct and indirect, correlated with the occurrence in the group of two kinds of ova, large and small. Direct development, in which the adult form is achieved without striking metamorphosis by a gradual succession of stages, seems to be confined to the family Balanoglossidae. ”

“ The vascular system does not readily lend itself to morphological comparison between such widely different animals as Balanoglossus and Amphioxus, and the reader is therefore referred to the memoirs cited at the end of this article for further details.
Reproductive System.—The sexes are separate, and when mature are sometimes distinguished by small differences of colour in the genital region. Both male and female gonads consist of more or less lobulated hollow sacs connected with the epidermis by short ducts. ”

“ The function of alimentation is closely associated with that of locomotion, somewhat as in the burrowing earthworm; in the excavation of its burrows the sand is passed through the body, and any nutrient matter that may adhere to it is extracted during its passage through the intestine, the exhausted sand being finally ejected through the vent at the orifice of the burrow and appearing at low tide as a worm casting. ”

“ Septal bars between two contiguous clefts, corresponding to the primary bars in Amphioxus; (2) Tongue-bars. The chief resemblances between Balanoglossus and Amphioxus in respect of the gill-slits may be stated briefly as follows:— (α) the presence of two kinds of branchial bars in all species and also of small crossbars (synapticula) in many species; (β) numerous gill-slits, from forty to more than a hundred pairs; (γ) the addition of new gill-slits by fresh perforation at the posterior end of the pharynx throughout life. ”