38 THE ZOOLOGIST. 



which have been reared through their metamorphosis, vary 

 remarkably in their inheritance of parental characters, even from 

 year to year. But far more remarkable than this is the fact 

 that different orders of Echinoidea can be crossed, whereas in 

 Vertebrates and Insects even separate families cannot be thus 

 treated. Professor MacBride has himself bred larva? from 

 Echinus esculentus and Echinocardium cordatum, though they 

 could not be kept alive longer than eight days. Most wonderiul 

 of all is the fact that echinoderm eggs can be fertilized by 

 mollusc sperm and yield larvae. 



It is found, moreover, that echinoderm eggs can be fertilized 

 by simply being treated with hypertonic sea-water, i. e. water in 

 which the normal proportion of chlorides is increased ; but the 

 segmentation in such cases is occasional and irregular, and the 

 larvae feeble, lying on the bottom. 



Professor MacBride has much of interest to say on the 

 subject of larvae more familiar to the ordinary naturalists. He 

 considers that the worm or grub type of larvae is really an 

 ancestral form, modified by the necessities of its environment, 

 and points out that the active larva of the Cockroach is 

 not really ancestral, but passes through a stage in the egg in 

 which it shows rudiments of abdominal limbs, recalling a worm- 

 shaped ancestor like a centipede. Abdominal limbs also occur 

 in Machilis, one of the most primitive insect order Tliysanura 

 (the Spring-tails). He points out that the most helpless and 

 worm-like larvae, those of the more specialized Diptera, are 

 practically in the position of parasites, and have lost their limbs 

 and even their jaws in consequence. The parallel might have 

 been carried farther ; for larvae of the caterpillar and maggot type 

 exhibit the peculiarity, noticeable in parasites, of being able to 

 live entirely on one kind of food, and preferentially doing so, 

 while many fly-maggots are actually parasitic in various ways, 

 from merely sucking the blood of the host to actually living 

 inside it. Altogether this book is one to be most warmly re- 

 commended to all naturalists. 



