140 ZOOLOGY. 



brain * and spinal cord, but sends oS a few nerves to tlic 

 periphery, with nerves to the two minute eye-spots. There 

 are no kidneys like those of the higher Vertebrates, but 

 glandular bodies which may serve as such. Tlie reproductive 

 ghxnds are square masses attached in a row on each side of 

 the walls of the body-cavity. The eggs 7nay pass out of the 

 mouth or through tlie pore. Kowalevsky found the eggs 

 issuing in May from the mouth of the female, and fertil- 

 ized by spermatic particles likewise issuing from the moutli 

 of the male. The eggs are very small, 0.10.5 millimetres 

 in diameter. The eggs undergo total segmentation, leav- 

 ing a segmentation-cavity which becomes the body-cavity. 



The blastoderm now invaginates and the embryo swims 

 about as a ciliated gastrula. The body is oval, and the 

 germ does not differ much in appearance from a worm, 

 star-flsh, or ascidian in the same stage of growth. No ver- 

 tebrate features are yet developed. 



Soon the lively ciliated gastrula elongates, the alimentary 

 tube arises from the primitive gastrula-cavity, while the 

 edges of the flattened side of the body grow up as ridges 

 which afterwards, as in all vertebrate embryos, grow over 

 and enclose the spinal cord. Wheii the germ is twenty-four 

 hours old it assumes the form of a ciliated flattened cylin- 

 der, and now resembles an Ascidian embryo, there being a 

 nerve-cavity, with an external opening, which afterwards 

 closes. The notocord appears at this time. 



In the next stage observed the adult characters had ap- 

 peared, the mouth is formed, the first pair of gill-openings 

 are seen, eleven additional pairs ajipearing. It thus appears 

 that wliile the lancelet at one time in its life presents 

 Ascidian features, yet, as Balfour states, "all the modes of 

 development fouml in tlie liigher Vertebrates are to be 

 looked upon as modilicaLions of that of Aniphioxus." 



* Langerbaiis lias fli^iired .an olfactory lobe; and all observers 

 agree tlial a ventricle is preseut; tbus tbere is a sligbt approximatiou 

 to a brain. 



